UNIVERSITY  OF  CALIFORNIA 
LOS  ANGELES 


, 


-^—^^ 

TRANSFORMERS. 


THEIR  THEORY,  CONSTRUCTION  AND 
APPLICATION,  SIMPLIFIED. 


BY  CARYL  D.  HASK1NS. 

ASSOCIATE     MEMBER     AMERICAN     INSTITUTE     OF 
ELECTRICAL    ENGINEERS. 


ILLUSTRATED. 


1892. 
BUBIER   PUBLISHING    COMPANY, 

LYNN,   MASS. 


COPYRIGHTED  BY 
BUBIER  PUBLISHING  COMPANY, 

LYNN,   MASS. 
1892. 


G.  H.  &  W.  A.  NICHOLS, 


Ttf 


DEDICATION. 


TO  MY  EARLIEST,  MOST  THOROUGH,  AND  MOST  VALUED 
IXSTICTOR  IN  PRACTICAL  ENGINEERING,  MY  FATHER, 
JOHN  F.  HASKINS,  M.  E.,  M.  I.  M.  E.,  M.  S.  A.,  ETC.,  THIS 
LITTLE  VOLUME  IS  RESPECTFULLY  DEDICATED. 


379385 


CONTENTS. 


DEDICATION. 

Page 

CHAPTER  1 9 

INDUCTION  AND  DISTRIBUTION  BY  ALTER- 
NATING CURRENT. 

CHAPTER  II 31 

THEORETIC  CONSIDERATIONS  OF  THE  TRANS- 
FORMER. —  NON-REGULATION. SELF-INDUC- 
TION.—  MUTUAL  INDUCTION. LOSSES,  FOU- 

CAULT  CURRENTS. — HYSTERESIS,  LEAKAGE. 

CHAPTER  III 55 

THE  THEORY  OF  THE  TRANSFORMER  MATH- 
EMATICALLY CONSIDERED. 

CHAPTER  IV 63 

EVOLUTION  OF  THE  ELECTRICAL  TRANS- 
FORMER. 

CHAPTER  V 73 

TRANSFORMER  CONSTRUCTION. 

CHAPTER  VI 96 

THE    TRANSFORMER    IN    SERVICE. 

CHAPTER  VII 110 

COMMERCIAL    TRANSFORMERS. 

APPENDICES 128 

GLOSSARY 143 

INDEX.  145 


PREFACE. 


It  has  often  been  observed  by  almost  every  member 
of  the  electrical  fraternity,  that  induction,  and  its  out- 
come, the  transformer,  is  to  the  popular  mind,  the 
greatest  mystery  of  the  whole  lighting  system  with 
which  they  come  in  contact. 

There  is  something  tangible  about  the  dynamo.  Its 
movement,  and  the  applied  power  are  apparent.  The 
lamp  glows,  and  its  action  is  appreciable,  but  the  trans- 
former remains  to  them  an  uncanny  mystery. 

So  too  the  average  electrician  whose  training  has 
long  accustomed  him  to  the  management  and  applica- 
tion of  the  electric  current,  finds  in  the  transformer  as 
a  rule,  more  points  regarding  which  his  mind  is  hazy 
and  uncertain,  than  in  any  other  one  piece  of  appara- 
tus with  which  he  has  to  deal. 

The  greater  part  of  the  printed  matter  dealing 
with  the  transformer  which  has  from  time  to  time 
appeared,  has  been  either  strictly  technical,  or  entirely 
popular. 

I  have  endeavored  in  the  following  pages  to  treat  of 
the  transformer  and  its  action  in  such  a  manner  as  to 
render  the  work  of  especial  value  to  the  central  sta- 
tion electrician,  the  student,  and  the  investigator, 


8  PREFACE. 

while  the  greatest  care  has  been  exercised  to  render 
the  matter  so  clear,  simple  and  interesting,  that  it  may 
come  within  the  scope  of  the  general  public,  and  meet 
the  demand  for  a  semi-technical,  and  yet  semi-popular 
treatise  on  the  Electrical  Transformer  which  has  not 
heretofore  been  obtainable. 

CARYL  D.  RASKINS. 

Boston,  August  1st,  1892. 


TRANSFORMERS. 


CHAPTER  I. 

INDUCTION    AND  DISTRIBUTION   BY  ALTERNATING 
CURRENT. 

BEFORE  taking  up  and  considering  in  detail  the 
calculation,  construction  and  use,  of  the  piece  of 
apparatus  which  forms  the  subject  matter  of  this 
treatise,  it  is  necessary  that  the  natural  laws  and 
commercial  necessities  which  lead  up  to  its  manu- 
facture and  application  should  be  briefly  con- 
sidered. It  has  been  thought  best  therefore,  to 
devote  a  preliminary  chapter  to  the  natural  phe- 
nomenon know  as  "Electrical  Induction,"  and*  to 
the  general  character,  functions,  and  application 
of  alternating  currents.  The  object  of  this  pre- 
liminary chapter,  of  necessity  renders  it  of  an 
elementary  nature,  but  it  can  scarcely  be  con- 
sidered superfluous,  as  it  deals  with  the  funda- 
mental principle  which  underlies  the  whole  subject. 
Since  certain  statements  must  in  the  consideration 
of  all  subjects  be  taken  for  established  certainties, 


10  TJRANSFOKMEKS. 

as  bases  for  future  argument,  let  us  consider  it  an 
axiom  that  all  electrical  currents  have  a  direction 
of  flow,  just  as  have  all  streams  of  water  or  cur- 
rents of  air.  To  render  the  idea  of  electricity 
more  thoroughly  consistent  with  our  mode  of 
thought,  it  will  be  found  preferable  to  cease  to 
consider  it  as  an  imperceptible  existence,  and  to 
treat  it  as  a  tangible  body ;  it  will  therefore  be 
dealt  with  and  regarded  as  a  subtle  fluid  through- 
out the  following  pages. 

It  is  a  recognized  fact  that  electricity  as  an 
imaginary  fluid  may  under  certain  conditions  be 
confined,  and  may  exist  in  inertia;  but  at  such 
times  it  is  generally  known  as  difference  of 
potential,  only  when  some  form  of  motion  results 
however,  does  electricity  become  manifest  to 
human  perception,  arid  then  only  within  certain 
ranges  and  under  certain  conditions. 

The  particular  function  of  electricity  with  which 
we  are  chiefly  to  deal  in  this  treatise  is  a  very 
remarkable  natural  law  known  as  Electrical  In- 
duction. Unlike  many  other  electrical  terms,  the 
word  induction  is  here  very  aptly  applied.  Induc- 
tion, the  noun,  from  the  verb  induce,  which  Webster 
defines  as  "  to  lead  or  influence  by  persuasion,  to 
actuate,  to  impel,  to  urge;"  "electrical  induc- 
tion" in  fact,  is  that  force  which  "persuades," 
"actuates"  or  "impels"  an  electrical  current  in 
one  body  by  the  influence  of  current  in  another. 


INDUCTION    AND  DISTRIBUTION.  11 

To  state  this  briefly  it  may  be  said,  that  whenever 
an  electrical  current  comes  into  existence  it  induces 
or  creates  a  current  in  all  surrounding  conductive 
masses,  in  a  direction  opposite  to  its  own.  During 
the  period  of  its  flow  in  uniform  quantity,  it  has 
no  inductive  influence  ;  the  period  of  flow  of  the 
induced  current  extending  only  over  a  time  equal 
to  that  between  the  commencement  and  attain- 
ment of  full  quantity  of  the  inducing  current. 
(This  statement  will  be  modified  later,  but  for  the 
present  it  may  be  safely  accepted.)  When  a 
current  ceases  it  induces  a  current  in  surrounding 
masses,  in  a  direction  similar  to  its  own. 

As  has  been  already  stated,  currents  are  induced 
in  "  all  surrounding  conductive  masses."  This  is 
strictly  true,  however  remote  these  masses  may  be. 
The  "  making  "  or  "  breaking  "  of  ever  so  insignifi- 
cant a  current  circuit  on  the  earth,  undoubtedly 
induces  currents  in  conductive  masses  on  the 
Moon,  but  since  the  inductive  influence  decreases 
as  the  square  of  the  distance,  the  effect,  even 
through  comparatively  small  intervals  of  space, 
becomes  inappreciable.  The  interval  of  time, 
between  the  commencement  of  the  current  flow  in 
the  inducing  circuit,  or,  as  it  is  generally  called, 
the  "  primary,"  and  the  commencement  of  flow  in 
the  induced  circuit,  or  secondary,  is  known  as  the 
"lag"  between  primary  and  secondary. 

Having  briefly  stated  the  general  character  of 


12  TRANSFORMERS. 

inductive  law,  it  will  be  well  to  consider  the  cause 
of  this  effect.  This  can  be  more  clearly  exempli- 
fied by  resorting  to  simile.  We  do  not  claim  the 
similes  as  original,  but  doubtless  none  more  plain 
or  conclusive  could  be  found. 

All  active  electrical  conductors  (for  convenience 
we  will  limit  our  consideration  of  the  matter  to 
wires,)  are  considered  to  be  surrounded  by  a  field 
of  force,  little  ripples  or  rings  of  energy,  concentric 
with  the  conductor,  extending  equally  in  all  direc- 
tions, and  becoming  less  and  less  intense  as  they  be- 
come more  and  more  remote  from  their  source. 
By  referring  to  diagram  No.  1,  this  may  be-  made 
more  clear.  Let  A  represent  a  section  through  the 
wire  or  conductor,  and  B,  B',  B"  the  lines  of  force 
surrounding  it ;  becoming  less  intense  as  they  be- 
come more  remote.  Now  the  theory  on  which  all 
inductive  electric  law  is  based  is :  That  whenever 
a  conductor  cuts  through  "  lines  of  force,"  or  vice 
versa,  when  "  lines  of  force  "  cut  through  a  con- 
ductor, a  current  is  set  up  in  that  conductor,  pro- 
vided always,  that  the  conductor  be  part  of  a 
closed  or  complete  circuit.  Current  effects  may 
in  reality  be  created  in  what  would,  generally 
speaking,  not  be  considered  a  complete  circuit. 
These  effects  are  known  as  "  Eddy "  or  "  Fou- 
cault "  currents,  the  former  term  exactly  defining 
their  character.  Further  consideration  will  be 
given  to  these  effects  in  a  later  chapter. 


INDUCTION  AND  DISTRIBUTION.  13 


i«i.  a. 


14  TRANSFORMERS. 

In  the  dynamo,  current  is  generated  by  moving 
conductors,  in  such  a  way  that  they  will  cut 
through  lines  of  force.  In  the  transformer,  current 
may  be  said  to  be  generated  by  moving  lines  of 
force,  in  such  a  way  that  they  will  cut  through 
conductors.  Thus,  in  one  sense,  the  dynamo  and 
the  transformer  may  be  said  to  be  opposites,  al- 
though in  reality  almost  identical  in  theory. 

We  will  now  endeavor  to  describe  this  whole 
matter  more  graphically.  It  should  be  borne  in 
mind  that  in  this,  as  in  all  similar  descriptions 
throughout  the  volume,  due  allowance  must  be 
made  for  the  liberty  which  is  taken  in  treating  of 
electricity,  lines  of  force,  etc.,  as  actual  palpable 
existences.  In  the  case  of  the  latter,  at  least,  we 
may  say  quite  frankly  that  they  are  simply  influ- 
ences which  have  been  universally  assumed  to 
plausibly  account  for  effects,  the  true  cause  of 
which  we  can  only  surmise.  As  has  already  been 
hinted,  it  is  only  the  effects  that  are  caused  by 
electricity  that  are  appreciable  to  us,  the  exact 
nature  of  the  subtle  influence  itself  is  no  more 
understood  today  than  it  was  when  the  ancient 
Greeks  discovered  the  effect  of  friction  upon 
amber,  and  christened  it  "Electron." 

Turning  to  Fig.  2,  let  us  consider  A  and  B 
to  be  electrical  conductors,  each  one  a  portion  of 
two  separate  complete  circuits.  A  current  springs 
into  existence  in  A,  the  primary  (no  matter,  for 


INDUCTION    AND   DISTRIBUTION.  .15 

the  present,  what  created  it).  Lines  of  force  are 
immediately  projected  into  the  surrounding  space, 
just  as  ripples  are  set  in  motion  on  the  surface  of 
water  by  a  falling  stone.  These  lines,  in  course 
of  projection,  must  of  necessity  cut  through  B,  the 
secondary.  This  induces  current  in  B.  Let  us 
suppose  that  the  current  in  A  is  flowing  towards 
us  ;  then  the  current  in  B  is  flowing  away  from  us. 
As  soon  as  the  current  in  A  becomes  fixed  in 
quantity,  and  the  lines  become  stationary,  the  cur- 
rent in  B  ceases.  Now  let  us  suppose  that  the 
current  in  A  ceases.  The  lines  of  force  immedi- 
ately collapse  upon  the  centre  B,  In  doing  this 
they  must  necessarily  cut  through  B  again,  but  in 
an  opposite  direction.  This  sets  up  a  second  cur- 
rent in  B,  also  in  an  opposite  direction  to  the  former 
one,  so  that  the  current  in  B  is  now  coming 
towards  us  ;  the  same  direction  that  the  current  in 
A  held  until  it  ceased.  Thus  it  will  be  seen,  that, 
as  has  already  been  stated,  when  an  electric  cur- 
rent comes  into  existence  it  induces  a  current  in 
neighboring  conductors,  in  a  direction  opposite  to 
its  own.  When  a  current  ceases  it  induces  a 
current  in  surrounding  conductors,  in  a  direction 
similar  to  its  own. 

Having  made  the  fundamental  principle  of  in- 
duction somewhat  clear,  we  may  now  give  some 
brief  consideration  to  the  system  of  electrical 
distribution,  which  this  remarkable  law  has  enabled 


16  TRANSFORMERS. 

man  to  formulate.  Generally  speaking,  it  may 
quite  safely  be  said  that  the  distribution  of  elec- 
tricity through  long  distances  is  not  economical, 
and  for  a  very  simple  reason.  The  loss  due  to 
electrical  resistance  of  the  conductors  must  be 
considerable,  since  C2R  =  watts  lost  in  transmis- 
sion. Where  C  =  Current  in  Amperes,  R==Resist- 
ance  of  Conductor  in  Ohms.  Thus  it  is  evident 
that  either  the  resistance  of  the  circuit  must  be 
kept  at  a  minimum,  or  the  current  strength  must 
not  be  great. 

The  first  of  these  two  alternatives  would  at  once 
necessitate  the  use  of  large  masses  of  copper  for 
conductors,  but  this  is  generally  precluded  by  the 
high  price  of  that  valuable  commodity.  The  other 
alternative,  then,  which  in  any  case  is  the  most 
desirable,  is  the  only  one  worthy  of  consideration 
from  a  commercial  standpoint. 

To  reduce  the  current  strength  or  volume,  and 
yet  retain  for  transmission  the  same  amount  of 
force  or  energy,  it  of  course  becomes  necessary  to 
increase  the  voltage  or  pressure.  In  this  respect 
electricity  is  quite  analogous  to  water — the  same 
amount  of  power  may  be  delivered  by  a  small 
stream  at  a  high  pressure,  as  by  a  large  stream 
with  small  head.  Thus  far,  then,  the  second  al- 
ternative presents  no  difficulty,  as  by  sufficiently 
increasing  the  pressure  and  reducing  the  current, 
high  powers  may  be  transmitted  through  long  dis- 


INDUCTION  AND  DISTRIBUTION.  17 

tances  without  the  use  of  large  quantities  of  cop- 
per and  without  excessive  loss. 

But  a  new  difficulty  now  presents  itself,  inas- 
much as  currents  of  high  pressure  are  extremely 
difficult  to  control  and  use  for  general  purposes ; 
besides  which  fact,  it  must  be  borne  in  mind  that 
contact  with  high  voltages  is  dangerous  and  some- 
times fatal  to  human  life.  Incandescent  lamps  have 
not  as  yet  been  so  constructed  as  to  operate  success- 
fully on  voltages  in  excess  of  200  volts,  which  may 
be  considered  low  pressure ;  whilst  even  if  the  lamps 
would  bear  higher  voltage,  such  careful  and  perfect 
insulation  would  be  necessary  as  to  render  their 
use  commercially  impracticable.  It  is  plain,  there- 
fore, that  the  very  pressure  which  renders  it  possi- 
ble to  carry  electrical  energy  economically  through 
long  distances,  would  render  it  practically  value- 
less, provided  there  were  no  way  to  reduce  it  at 
points  of  application  without  serious  loss. 

Induction  provides  us  at  once  with  a  means  of 
accomplishing  this  ;  as  by  proportioning  the  amount 
of  wire  in  inducing  and  induced  circuits,  the 
energy  delivered  at  a  high  pressure  on  the  primary, 
may  be  transformed  to  a  reduced  pressure  and 
greater  volume  in  the  secondary,  or  vice  versa. 
This  can  of  course  only  be  accomplished  by  the 
use  of  intermittent,  pulsating  or  alternating  cur- 
rents ;  any  or  all  of  which  will  produce  the  pulsa- 
tions of  the  lines  of  force,  which  forms  the 


18  TRANSFORMERS. 

fundamental  principle  of  induction.  The  electric 
current  which  was  first  applied  to  incandescent 
lighting,  was  the  direct,  flowing  constantly  and 
uninterruptedly  in  one  direction.  This  class  of 
current  does  not  of  course  permit  of  the  use  of 
induction  for  transformation,  and  has  therefore  to 
be  distributed  at  useful  or  low  pressures,  which  as 
we  have  seen  renders  it  wasteful  for  long  distance 
work. 

As  has  just  been  stated,  distribution  by  pulsat- 
ing or  alternating  current,  renders  it  possible  to 
adjust  the  potential  at  any  given  point  to  any 
voltage,  without  serious  loss.  In  practice  how- 
ever, only  one  of  these  classes  of  current  is 
practicable,  and  this  for  reasons  which  will  be 
presently  stated,  is  the  alternating.* 

It  m&y  be  well  however,  before  going  further,  to 
make  plain  the  difference  between  the  pulsating 
and  the  alternating  current.  To  state  this  quite 
plainly,  it  may  be  said  that  a  pulsating  current  is 
one  which  starts  into  existence  in  direction  "a" 
Fig.  3,  dies  down,  more  or  less  rapidly,  then 
comes  into  existence  again  in  the  same  direction.^ 
We  have  endeavored  to  make  this  a  trifle  more 
explicit,  by  the  use  of  the  diagram,  the  arrows 

*This  statement  is  made  in  a  general  way;    there  is  at  least  one 
marked  exception  to  the  general  rule. . 

.  t"  Pulsating,"  "  intermittent,"  "  vibratory,"  "  interrupted,"  etc.,  are 
all  names  in  common  use  for  various  modifications  of  the  same  class 
of  current. 


INDUCTION  AND  DISTRIBUTION.  19 

showing   the   direction   of    current    flow   during 
different  periods. 

In  the  technical  consideration  of  alternating  and 
intermittent  currents,  a  system  of  "curve"  draw- 
ing is  used,  whereby  every  rise  and  fall  of  current, 
every  break  and  every  alternation  is  accurately 
set  forth.  This  system,  which  is  almost  invaluable 


in  all  work  connected  with  alternating  or 
fluctuating  currents,  we  will  only  briefly  describe, 
as  it  is  in  general  use,  and  almost  all  are  familiar 
with  it.  Let  us  suppose  that  we  have  a  rectangle, 
the  surface  of  which  is  divided  into  very  minute 
squares  by  vertical  and  horizontal  lines.  In  draw- 
ing a  curve  showing  the  fluctuations  of  an  alter- 
nating current,  the  distance  between  the  vertical 


TRANSFORMERS. 


lines,  or,  as  they  are  technically  termed,  "Ordi- 
nates,"  should  be  considered  as  fractions  of  time 
(generally  taken  in  decimals  of  a  second  or  min- 
ute), whilst  the  "  Abscissae,"  or  distance  between 
the  horizontal  lines  represent  amperes  (or  fractions 
of  current.)  Two  such  curves  are  here  represented. 
The  "cross  sectioning"  is  not  shown,  it  being 
really  unnecessary  for  purposes  of  description. 

Fig.  4  represents  an  intermittent  current. 
The  line  A  B  is  the  neutral  line,  and  where  the 
curve  line  touches  this,  no  current  is  flowing.  The 
portion  of  the  curve  above  A  B  indicates  that  the 
current  is  flowing  in,  say  a  -J-  direction,  whilst 
when  the  curve  passes  below  the  line,  the  current  is 
indicated  as  flowing  in  a  direction  opposite  to  that 
which  is  held  when  the  curve  was  above  the  line — 
or  is  flowing  in,  say  a  —  direction.  A  B  is  con- 
sidered as  0,  the  amperes  being  numbered  each 
way  from  it,  those  above  being  in  one  direction, 
those  below  in  another. 

It  will  be  easy  to  imagine  by  casting  the  eye 
upon  the  upper  curve,  ( the  pulsating  current ) 
Fig.  4,  how  the  lines  of  force  will  alternately  be 
projected  from  and  collapse  upon  the  primary 
conductor,  cutting  surrounding  conductors  and 
inducing  currents  in  them.  The  distance  between 
the  points  where  the  curve  touches  the  0  line  A 
B,  shows  us  the  length  of  duration  of  one  period, 
or  the  speed  with  which  the  current  is  alternately 


INDUCTION  AND   DISTRIBUTION. 


21 


22  TRANSFOKMEKS. 

"  made  "  and  broken,  whilst  the  distance  between 
the  0  line  and  the  maximum  elevation  of  the  curve, 
show  us  the  maximum  current  strength.  These 
curves  are  more  often  drawn  to  show  the  pressure 
waves,  in  which  case  of  course,  the  abscissae 
indicate  volts  ;  or  to  show  the  power  curve,  the 
product  of  pressure  and  current  (Cx  V=  watts)  in 
which  case  the  abscissae  become  watts. 

The  same  general  discription  applies  equally 
well  to  the  alternating  curve  shown  in  the  lower 
position,  Fig.  5.  It  is  only  necessary  to  bear  in 
mind  the  fact  that  where  the  curve  line  crosses  the 
0  line,  first  a  cessation  and  then  a  reversal  of 
direction  of  current  flow  is  indicated.  It  may  be 
well  to  state  that  these  lines  follow  very  closely 
the  rule  of  "  sine "  curves.  We  will  make  no 
attempt  to  discuss  the  theory  of  the  sine  curve  as  it 
has  been  thought  best  to  confine  the  mathematics 
in  this  treatise  exclusively  to  the  principle  and 
theory  of  the  transformer.* 

We  may  now  return  to  our  more  immediate  sub- 
ject, and  point  out  why  the  alternating,  as  com- 
pared with  the  pulsating  current,  is  the  only 
commercially  practicable  means  of  distributing 
large  quantities  of  energy  by  the  induction  system. 
At  first  this  seems  rather  incongruous,  since  we 
have  already  seen  that  the  pulsating  and  the  alter- 

*  For  a  concise,  simple  and  clear  elucidation  of  the  "  sine  curve  "  we 
would  refer  the  reader  to  Messrs.  Slingo  &  Brooker's  "  Electrical  Engi- 
neering," an  excellent  work. 


INDUCTION   AND   DISTRIBUTION.  23 

nating  current  will  "induce"  equally  well  and 
efficiently,  the  former,  in  fact,  probably  more  effi- 
ciently under  certain  conditions. 

First  and  most  important  in  considering  this 
question,  we  must  remember  that  the  natural  out- 
come of  the  dynamo-electric  machine  is  an  alter- 
nating current.  It  is  the  commutator,  quite  a 
distinct  portion  of  the  dynamo,  which  serves  to 
"  straighten "  the  current,  and  the  commutator 
might  quite  as  well  be  a  distant  machine,  quite 
separate  from  the  dynamo,  so  far  as  theory  is  con- 
cerned. It  is  only  mechanical  considerations  and 
convenience  which  have  caused  it  to  be  incorpo- 
rated in  that  machine.  The  function  of  the 
commutator,  in  fact,  is  simply  to  reverse  the  con- 
nections at  the  same  instant  that  the  direction  of 
current  flow  reverses,  that  is  all.  We  may  illustrate 
this :  Suppose  there  were  two  tanks  full  of  water, 
as  illustrated  in  Fig.  6-1,  A,  B,  A  being  higher  than 
B,  and  that  these  two  tanks  were  connected  by  a 
long  rubber  tube,  easily  removable  from  spickets, 
and  that  you  held  the  end  of  the  tube  at  X  in  the 
left  hand,  and  the  end  Yin  the  right;  the  water 
would  be  running  from  J.,  through  the  tube  in  the 
direction  of  the  arrow.  Now  suppose  B  were 
suddenly  lifted  higher  than  A,  but  at  the  same 
instant  you  pulled  the  end  of  the  tube  X  off  of  A 
spicket,  and  thrust  it  on  to  B,  and  vice  versa  with 
the  end  y,  then  the  direction  of  flow  would  be 


24 


TRANSFORMERS. 


INDUCTION   AND  DISTRIBUTION.  25 

maintained  the  same  in  the  tube.  It  is  just  the. 
function  of  your  hands  here  that  the  commutator 
performs  for  the  dynamo. 

If  the  commutator  was  omitted,  and  collector 
rings  substituted,  we  should  have  an  alternating 
current  output,  easier  to  get  than  the  direct,  but 
not  at  first  used  because  supposed  to  be  less  man- 
ageable. 

On  the  other  hand,  to  get  a  pulsating  current 
we  must  either  have  a  dynamo  of  special  construc- 
tion, or  we  must  have  an  interrupter  or  circuit 
breaker  which  will  vibrate  very  rapidly,  alternate- 
ly opening  and  closing  the  circuit.  This  latter 
device  is  obviously  only  practicable  with  low 
voltages,  for  with  high  potentials  constant  arcing, 
and  speedy  destruction,  would  inevitably  result. 

Much  attention  has  been  given  of  late  by  a 
number  of  the  world's  best  electricians,  to  the 
special  dynamos  already  mentioned  as  being  de- 
signed to  generate  pulsating  currents,  and  consid- 
erable advance  has  been  made  in  this  direction. 
The  system  would  present  at  least  one  marked 
advantage,  provided  it  could  be  reduced  to  a  basis 
equally  efficient  with  the  alternating.  It  would 
permit  of  the  distribution  of  power  to  electric 
motors,  as  well  as  for  lighting  purposes,  a  use  to 
which  alternating  current  has  not  as  yet  been 
applied  with  any  marked  degree  of  success,  except 
in  very  small  powers ;  in  fact,  the  use  of  the 


26  TRANSFORMERS. 

alternating  current  is  practically  confined  today 
to  the  distribution  of  light,  and  to  a  few  special 
purposes,  such  as  electric  welding,  etc. 

It  is  easy  to  convert  mechanical  energy  into  elec- 
trical energy  in  the  form  of  alternating  current,  but 
it  is  most  difficult  to  convert  alternating  current 
energy  back  again  into  mechanical  energy  or  motion 
with  any  degree  of  efficiency. 

Pulsating  or  interrupted  currents  are  largely 
used  in  connection  with  batteries  and  induction 
coils,  where  but  small  amounts  of  energy  are  to  be 
dealt  with,  but  not  in  connection  with  lighting 
work.  Inductive  coils  and  transformers,  are 
practically  the  same  thing,  the  former  term  is 
used  in  relation  to  coils  for  raising  low  potentials 
to  high,  especially  where  the  powers  dealt  with  are 
small,  almost  always  in  conjunction  with  batteries. 
Where  large  powers  are  raised  to  higher  potentials, 
the  coils  are  generally  spoken  of  as  Step-Up  Trans- 
formers, which  are  treated  of  quite  exhaustively 
in  an  appendix.  The  term  Transformer,  or  as  it  is 
frequently  called  (especially  in  Europe)  Converter, 
is  used  to  specify  coils  intended  for  reducing  high 
potentials  to  lower.  Induction  coils  are  exten- 
sively used  in  conjunction  with  batteries  and  an 
interrupter,  for  experimental  work,  medical  pur- 
poses, electric  gas  lighting,  the  explosion  of 
blasts,  etc.  They  will  be  treated  of  in  the  following 
pages  only  in  the  most  cursory  manner,  they  are 


INDUCTION   AXD   DISTRIBUTION.  27 

most  ably  described  in  a  number  of  existing 
volumes,  and  scarcely  come  within  our  subject 
matter.* 

Distribution  by  alternating  current  and  trans- 
former is  commonly  accomplished  by  the  multiple 
or  parallel  system.  Fig.  7  shows  quite  clearly  the 
relative  positions  of  dynamo  and  transformer  when 
the  latter  are  placed  in  multiple ;  with  this  arrange- 
ment the  primary  circuit,  (and  each  secondary 
also,)  has  a  constant  potential,  the  amount  of  cur- 
rent varying  with  the  load.  Transformers  have 
also  at  times  been  arranged  in  series,  that  is  one 
after  another,  as  for  example  in  the  old  Jabloch- 
koff  system  of  arc  lighting,  but  this  arrangement 
is  not  common,  and  has  only  been  used  in  connec- 
tion with  lighting  service  for  street  and  arc  lights. 
The  series  arrangement  is  clearly  shown  in  Fig.  8. 
With  the  series  system  the  potential  is  variable 
with  the  load,  and  the  current  constant. 

The  series  and  multiple  arrangements  of  trans- 
formers may  be  clearly  defined  as  follows  :  When 
transformers  are  placed  in  series  the  same  current, 
and  whole  current,  passes  through  the  primary  of 
each  transformer  one  after  another,  and  then  back 
to  the  dynamo. 

When  transformers  are  arranged  in  multiple,  a 
certain  proportion  of  the  entire  current  passes 

*  For  information  relating  to  induction  coils,  the  author  refers  the 
reader  to  "Electricity  and  its  Recent  Applications,"  by  Edward 
Trevert. 


28 


TRANSFORMERS. 


INDUCTION   AND  DISTRIBUTION. 


TRANSFORMERS. 


from  the  mains  through  each  transformer  primary 
individually,  and  thence  back  to  the  dynamo.  If 
a  single  primary  burn  out  or  break  with  the  series 
system,  all  of  the  lights  go  out,  for  the  main  cir- 
cuit is  open.  (Special  devices  are  however  made 
to  provide  for  this  contingency.)  If  a  primary 
burns  out  with  the  multiple  arrangement  only  the 
lights  on  that  particular  transformer  go  out,  or  if 
the  main  circuit  is  broken  anywhere  along  the  line, 
then  only  those  transformers  which  are  beyond  the 
break  from  the  dynamo  cease  to  operate.  The 
lights  which  are  between  the  dynamo  and  the 
break  still  continue  to  burn. 

The  multiple  system  is  the  only  one  in  common 
use,  and  is  the  one  with  which  we  shall  chiefly 
deal.  The  pressures,  or  voltages  (primary),  which 
are  in  common  use  are  1000,  2000  and  2500  volts, 
and  in  a  few  cases  5000  volts.  Yet  higher  voltages 
than  these  are  in  use  in  Europe,  but  with  these 
very  high  pressures  proper  insulation  becomes  a 
very  difficult  problem. 


THEORETIC   CONSIDERATIONS.  31 


.    CHAPTER  II. 

THEORETIC  CONSIDERATIONS  OF  THE  TRANS- 
FORMER.—  IRON. —  REGULATION.  —  SELF-INDUC- 
TION. —  MUTUAL  INDUCTION.  —  LOSSES.  —  FOU- 
CAULT  CURRENTS. — HYSTERESIS. — LEAKAGE. 

IN  the  preceding  chapter  we  have  reviewed  the 
principle  and  characteristics  of  induction,  "and  the 
necessities  and  advantages  which  have  led  up  to 
the  use  of  the  alternating  current  and  the  trans- 
former, as  an  economic  means  for  the  distribution 
of  light.  We  will  now  endeavor  to  treat  some- 
what in  detail  those  various  influences  which  serve 
to  modify  or  enhance  the  phenomenon  which  we 
have  already  described. 

As  we  have  already  seen,  the  creation  or  stop- 
page of  a  current  in  a  conductor  will  induce  a 
current  in  surrounding  conductors,  and  it  is  known 
that  this  induction  is  subject  to  definite  and  known 
laws. 

It  is  obvious  that  to  bring  long  lengths  of  wire 
into  one  another's  useful  inductive  influence,  or 
"field  "  some  other  means  must  be  adopted  than 
that  of  stretching  them  side  by  side  through  a  long 
distance,  for  this  would  be  thoroughly  impracti- 


32  TRANSFORMERS. 

cable,  neither  would  this  serve  the  purpose,  even 
if  convenient,  for  experiment  has  shown  that  the 
resistance  of  the  two  circuits  being  consistent,  the 
voltage  in  the  primary  and  secondary  is  almost 
exactly  proportional  to  the  respective  lengths  of 
the  two  circuits  within  one  another's  influence. 
Thus  we  may  say,  to  state  this  arithmetically,  that: 

As  influencing  length  primary  :  Influenced 
length  secondary  :  :  Voltage  primary  :  Voltage 
secondary. 

Now  to  bring,  say  ten  feet  of  secondary,  into  the 
equal  influence  of  one  hundred  feet  of  primary, 
both  stretched  in  a  straight  line,  is  obviously  im- 
possible. It  has  been  found  necessary  and  most 
desirable  in  practice,  therefore,  to  make  the  two 
wires  into  coils,  placed  one  next  to,  or  one  over 
the  other  (see  Fig.  9).  In  this  way  it  is  perfectly 
easy  to  bring  a  long  wire  into  equal  influence 
throughout  its  length,  upon  a  short  wire,  A  A 
being  the  short  wire,  the  secondary  (generally 
speaking,)  and  B  B  the  primary,  or  long  wire. 
But  here  is  met  a  new  contingency,  that  of  self- 
induction.  Let  us  consider  this  same  coil  (Fig.  9) 
in  section  Fig.  10.  It  is  quite  obvious  that  the 
lines  of  force  projected  from  any  turn  of  the  pri- 
mary B,  must  cut  and  influence,  not  only  the 
neighboring  turns  of  the  secondary  A  A,  but  also 
the  neighboring  turns  of  itself,  thereby  setting  up 
an  influence  in  itself,  in  direct  opposition  to,  and 


THEORETIC   CONSIDERATIONS. 


34  TRANSFORMERS. 

tending  to  nullify,  the  primary  influence.  Sup- 
posing for  an  instant  that  the  secondary  coil  were 
absent,  leaving  the  primary  to  act  solely  upon 
itself,  turn  upon  turn,  and  supposing  that  nothing 
is  lost  in  induction,  or  in  other  words,  that  the 
efficiency  be  100  per  cent,  then  the  induced  in- 
fluence, the  counter  or  opposing  pressure  (the 
"counter  electro-motive  force,"  as  it  is  called), 
should  exactly  equal  the  initial  primary  force — 
one  hundred  units  of  force  pushing  against  one 
hundred,  and  nothing  would  flow  in  the  primary. 
A  coil  of  this  kind  is  used  for  some  purposes,  being 
known  as  an  inductive  resistance.  At-the  first 
glance  this  would  seem  to  entirely  destroy  the 
value  of  the  transformer,  but  in  reality  it  plays  a 
most  useful  and  important  part  when  modified  by 
the  influence  of  mutual  induction,  as  we  shall 
presently  see  when  considering  the  question  of 
regulation. 

Referring  again  to  Fig.  10,  we  will  now  consider 
the  part  which  the  secondary  coil  plays.  We  have 
already  seen  how  the  primary  induces  current  in 
the  secondary,  and  opposing  force  by  self  induc- 
tion within  itself.  It  is  obvious  that  since  the 
primary  coil  induces  current  in  the  secondary,  by 
reason  of  the  lines  of  force  projected  from  and 
retracted  to  itself,  the  secondary  coil  must  in  its 
turn  react  by  induction  upon  the  primary  as  soon 
as  it  becomes  active,  and  this  reactive  induction  of 


THEORETIC  CONSIDERATIONS.  35 

the  secondary  upon  the  primary  is,  of  necessity, 
favorable  to  and  in  the  same  direction  as  the  prime 
current  of  the  primary  coil  and  in  direct  opposi- 
tion to,  and  tending  to  nullify  the  effect  of  the 
self-induction  in  the  primary.  Meantime  however, 
the  secondary  has  set  up  within  itself,  by  its  self- 
induction,  a  force  in  opposition  to  its  prime  or 
useful  current,  which  is  again  practically  nullified 
by  the  induction  from  the  primary.  Thus,  the  two 
coils  act  and  react  upon  themselves  and  one 
another,  the  reaction  of  a  coil  upon  itself,  being 
termed  as  we  have  already  said,  self-induction,  and 
that  of  one  coil  upon  the  other,  which  we  have 
just  discribed,  mutual  induction.  The  two  terms 
are  sufficiently  indicative,  being,  in  fact,  almost 
descriptive  of  their  relative  action. 

On  these  two  factors  of  self  and  mutual  induc- 
tion, chiefly  depends  the  successful  operation  of 
the  transformer,  for  upon  them  alone  rests  the  self- 
regulation  of  the  transformer ;  without  regulation 
it  would  be  practically  useless,  because  wasteful 
and  inefficient. 

Transformer  regulation  is  simple  and  readily 
understood,  and  its  presence  amounts  to  a  ne- 
cessity. 

In  Fig.  11,  we  show  a  transformer  which  we 
will  suppose  to  be  in  operation,  P  is  the  primary 
supplied  from  an  active  circuit,  through  which 
current  is  constantly  flowing.  S  is  the  secondary, 


TRANSFORMERS. 


Pifc.il 


1 


.  12. 


THEOKETIC   CONSIDERATIONS.  37 

i.  e.  lamp  circuit,  and  L  L  are  lamps.  The  primary 
and  secondary  are  separated  from  one  another 
solely  to  render  the  diagram  more  distinct. 

It  is  evident  that  if  the  amount  of  current 
flowing  through  P,  were  dependent  solely  upon  its 
so-called  " dead  resistance"  or  the  Ohms*  in  its 
circuit,  then  the  same  amount  of  energy  would  be 
expended  in  it  continuously,  whether  the  lamps  in 
Sr  circuit  were  burning  or  not,  this  would  be  ex- 
tremely wasteful  for  the  dynamo,  and  therefore  the 
engines  at  the  station  would  be  doing  just  as 
much  work,  and  just  as  much  coal  would  be  burned 
when  no  lights  were  turned  on,  as  when  all  were 
in  use.  Then  too,  so  little  current  could  be  per- 
mitted to  pass  through  P,  that  it  could  be  practi- 
cally of  no  use  in  transferring  energy  to  S.  Here 
self-induction  comes  into  play.  Supposing  all  of 
the  lamps  (.Z/)  to  be  turned  off,  S  is  obviously  an 
"  open  "  or  an  incomplete  circuit,  and  no  current 
can  traverse  it.  The  self-induction  of  P  then  has 
full  play  to  react  on  P  coil,  choking  down  the 
prime  current  to  almost  nil,  the  amount  of  power, 
in  fact  present  in  P  being  about  equal  to  the  dif- 
ference in  energy  between  the  prime  current  on 
full  load  and  the  reaction  of  self-induction. 

This  difference  represents,  practically,  the  losses 
in  the  transformer,  with  which  we  shall  presently 

*  For  a  definition  of  terms  which  may  be  unfamiliar  to  the  non- 
electrical reader,  see  glossary  at  end  of  volume. 


73385 


88  TRANSFORMERS. 

deal,  almost  all  resulting,  however,  directly  or  in- 
directly in  heat.  The  engine  and  dynamo  are, 
therefore,  doing  very  little  work  at  this  point, 
when  no  lights  are  in  use. 

Now  suppose  one  light  is  turned  on  in  S  circuit. 
A  little  current  now  flows  in  $,  dependent  upon 
the  resistance  of  S  circuit.  This  sets  up  a  slight 
mutual  inductive  reaction  of  S  upon  P,  counter- 
balancing a  portion  of  the  self-induction  of  the 
primary.  More  current  flows  in  P,  and  the  engine 
and  dynamo  are  doing  just  that  much  more  work. 
And  so  the  action  goes  on,  as  light  by  light  is 
brought  into  service,  till  at  full  load  (or  the  point 
of  safe  carrying  capacity  of  the  two  wires)  the 
self-induction  of  the  primary  is  proportionally 
balanced  by  mutual  induction.  If  the  secondary 
coil  were  short  circuited,  as  frequently  happens, 
that  is,  if  the  two  ends  of  S  were  joined  without 
intervening  resistance,  such  as  lamps,  then  more 
current  would  pass  than  the  wire  could  stand,  and 
it  would  melt  in  two  at  its  weakest  point,  quite  as 
likely  in  the  primary  as  the  secondary.  The  same 
thing  would  happen  if  too  many  lamps  were  placed 
in  the  secondary. 

To  prevent  the  destruction  of  transformers  in 
this  way  "  fuses  "  are  introduced,  both  in  the  pri- 
mary and  the  secondary  circuits.  A  fuse  is  a  short 
piece  of  soft,  easily  fusible  metal,  usually  lead  and 
tin,  calculated  to  melt,  and  thus -break  the  circuit 


before  the  danger  limit  of  the  winding  or  wire  is 
reached.  When  a  fuse  burns  out,  or  *'  blows,"  all 
of  the  lights  go  out  which  are  on  that  transformer, 
but  nothing  is  injured. 

The  reader  may  have  wondered  why  the  curve 
of  rise  and  fall  of  current  shown  in  Fig.  5  of  pre- 
vious chapter  did  not  abruptly  break  and  com- 
mence, instead  of  gradually  waxing  and  waning. 
This  effect  is  due  almost  wholly  to  self-induction, 
and  may  be  now  readily  understood.  Self-induc- 
tion may,  in  this  connection,  be  looked  upon  as  a 
kind  of  electrical  inertia.  A  most  ingenious 
device,  known  as  a  reactive  coil,  and  used  for  turn- 
ing lights  up  or  down  to  any  required  brilliancy, 
is  dependent  for  its  action  solely  upon  the  effects 
of  mutual  and  self-induction.  It  will  be  found 
fully  described  later,  for  it  is  an  excellent  example 
of  these  effects. 

But  we  cannot  deal  with  it  until  we  have  con- 
sidered a  matter  on  which  we  have  not  yet 
to  ached,  but  which  is  of  prime  importance:  namely, 
the  presence  of  iron  in  the  transformer;  on  this 
entirely  depends  the  efficient  application  of  the 
phenomena  already  discribed. 

We  have  dealt  with  electrical  currents  and  their 
direction  of  flow:  we  must  now  introduce  a  new 
factor,  that  of  magnetic  currents,  heretofore  spoken 
of  as  lines  of  force.  These  are  quite  distinct  from 
electric  currents,  but  they  go  hand  in  hand,  the 


40  TRANSFORMERS. 

one  being  dependent  upon  the  other.  Like  electric 
currents  they  have  (  we  suppose )  a  direction,  we 
can  scarcely  say  a  direction  of  flow.  Every 
known  medium,  even  a  vacuum  is  a  conductor,  but 
average  iron  is  some  700  times  better  than  any 
other  known  substance,  all  other  mediums  being 
about  equal,  save  some  comparatively  rare  metals 
of  the  iron  group,  such  as  nickel,  cobalt,  etc. 

The  direction  of  movement  of  these  lines  of 
magnetic  force  is  at  right-angles,  to  the  direction 
of  current  flow,  as  shown  at  Fig.  12.  With  a 
single  wire  this  "field  "  consists,  as  we  have  already 
seen,  of  concentric  lines  of  force  rotating  around 
the  conductor.  These  lines  of  force  are  of  course 
purely  imaginary,  but  something  must  be  assumed 
to  render  the  phenomena  of  electro-magnetism 
capable  of  being  grasped.  A  very  pretty  demon- 
stration of  the  presence  of  the  force  which  we 
term  magnetism  may  be  made  by  thrusting  a  wire 
through  a  card,  and  then  sprinkling  the  card  freely 
with  fine  iron  filings.  On  passing  current  through 
the  wire,  the  filings  will  arrange  themselves  in 
concentric  circles  around  the  wire,  exactly  as  we 
have  described  and  shown  in  Chapter  I. 

Magnetic  resistance  is,  in  its  way  quite  as  dis- 
astrous to  efficient  operation,  as  is  electrical ; 
the  magnetic  conductivity,  or  as  it  is  termed  the 
permeability  of  the  medium  through  which  the 
lines  of  force  are  to  be  forced  or  circulated,  has 


THEORETIC   CONSIDERATIONS.  41 

everything  to  do  with  the  economical  operation 
of  all  electro-magnetic  apparatus.  Thus  in  Fig. 
12,  No.  2,  a  single  coil  of  live  wire,  the  circulation 
of  magnetic  lines  will  be  about  as  indicated  by 
the  arrows.  Now  if  this  coil  be  simple  wire 
wound  up  hollow,  or  on  wood,  or  brass,  or  in  fact 
any  substance  other  than  metals  of  the  iron  group, 
then  it  will  take,  roughly  speaking,  some  700 
times  the  electrical  energy  in  the  coil  to  maintain 
a  given  strength  of  magnetic  circuit  that  it  would 
if  the  magnetic  circuit  were  of  iron  of  sufficient 
sectional  area.  The  intensity  of  the  magnetic  circuit 
is  generally  expressed  by  the  number  of  "Kapp 
lines  "  per  square  inch  of  section,  in  other  words 
the  strength  of  the  magnetic  circuit,  is  supposed 
to  increase  according  to  the  proximity  of  the  lines 
to  one  another,  that  is,  with  the  number  within  a 
given  sectional  area.  It  is  obvious  therefore  that 
in  constructing  a  transformer,  the  path  for  the 
magnetic  circuit  must  be  a  complete  circuit  of 
iron*  if  the  apparatus  is  to  be  efficient. 

As  the  resistance  of  the  magnetic  circuit  in- 
creases with  the  length,  this  must  of  course  be 
kept  as  short  as  possible,  consistent  with  good 
mechanical  construction.  The  permeability  of 
iron  also  varies  very  greatly;  this  may  be  expressed 
by  the  number  of  Kapp  lines  per  square  inch,  per 

*  This  theory  is  contradicted  provisionally  by  the  inventor  of  the 
"  Hedgehog  "  transformer,  for  which  see  appendix. 


42  TRANSFORMERS. 

ampere  turn*  in  a  given  length  of  magnetic  cir- 
cuit. Therefore  it  is  necessary  for  the  best 
results,  to  select  iron  of  the  greatest  magnetic 
permeability,  that  is  iron  in  a  given  sectional  area 
of  which  the  greatest  number  of  Kapp  lines  can  be 
induced  with  the  least  expenditure  of  energy. 

The  number  of  lines  per  square  inch  does  not 
increase  in  a  direct  ratio  with  the  number  of 
ampere  turns;  there  is  a  point  at  which  the  number 
of  ampere  turns  must  be  vastly  increased  to  secure 
even  a  slight  increase  of  magnetic  strength,  and 
it  is  evident  that  it  could  be  neither  economical 
nor  advantageous  to  build  commercial  apparatus 
to  work,  at,  or  above,  this  magnetic  strength.  The 
point  at  which  the  greatest  number  of  lines  per 
square  inch  can  be  induced  with  a  relatively 
economical  expenditure  of  current,  is  obviously 
the  best  magnetic  strength  to  use  in  commercial 
apparatus.  This  is  known  as  the  "  working  point " 
of  the  iron,  and  varies  greatly  with  the  grade  of 
material. 

There  is  also  another  point,  at  which  the  mag- 
netic strength  practically  ceases  to  increase, 
irrespective  of  any  increase  of  ampere  turns. 
This  is  the  "  point  of  saturation."  At  this  point  the 
number  of  Kapp  lines  per  square  inch  of  section 
have  reached  the  limit  of  that  particular  piece  of 

*  One  complete  turn   of  wire  carrying  one  ampere,  or  two  turns 
carrying  J  an  ampefe,  etc. 


THEOKETIC   CONSIDERATIONS.  43 

iron.     The  point  of  saturation  is  never  reached  in 
commercial  transformer  practice. 

In  testing  iron,  all  of  the  above  characteristics 
are  clearly  expressed  by  plotting  curves,  similar  to 
that  shown  in  Fig.  13. 

This  curve  shows  wrought  iron,  having  excel- 
lent qualities  for  transformer  construction;  its 
magnetic  strength  increases  rapidly  up  to  the 
working  point  as  compared  with  the  rate  of  increase 
of  magnetic  turns  to  obtain  the  result.  It  is  of 
course  understood  by  the  reader  that  the  greater 
the  density  of  lines  of  force  in  the  iron,  the  greater 
the  energy  induced  in  the  secondary.  Herein  lies 
the  whole  question  of  transformer  proportioning. 
How  many  turns  in  the  primary,  how  many  turns 
in  secondary,  and  what  section  of  iron  to  obtain 
certain  results  ?  This  will  be  dealt  with  practi- 
cally and  theoretically  further  on. 

Cast-iron  gives  the  poorest  results  and  is  never 
used  for  transformers.     Soft  rolled  charcoal  iron 
has  generally  been  considered   the  best,  but  the  A 
most  recent  practice  seems  to  indicate  that  some  |i\ 
grades  of  very  soft  rolled  steel  have  the  highest J  \ 
efficiency  of  all  magnetic  mediums — iron,  however, 
is  generally  used. 

A  transformer  constructed  with  cast-iron  would 
be  comparatively  inefficient,  or  else  the  iron  would 
have  to  be  so  increased  in  sectional  area  to  obtain 
the  necessary  number  of  total  Kapp  lines,  that 


TBAN8FOEMEB8. 


I 


THEORETIC   CONSIDERATIONS.  45 

bulk  and  weight  would  be  prohibitively  large.  In 
other  words,  the  working  point  of  this  iron  is  far 
too  low. 

Before  considering  transformer  losses,  mention 
should  be  made  of  the  reactive  coil  already  referred 
to,  for  in  it  is  embodied  a  practical  illustration  of 
the  application  of  all  of  the  laws  as  yet  referred  to. 

Fig.  14  shows  one  of  these  coils,  which  consists 
of  three  main  portions,  a  ring  of  iron  highly  lami- 
nated (^4.),  around  which  is  wound  a  considerable 
number  of  turns  of  wire,  in  series  with  the  primary 
or  secondary  circuit  which  it  is  to  control.  A 
circular  block  or  plug  of  iron  (.#),  a^so  highly 
laminated,  fitting  closely,  but  without  touching, 
into  the  hole  through  A,  and  supported  and  rotat- 
ing in  bearings  at  F.  A  solid  copper  casting  ((7), 
forming  a  complete  secondary  circuit  of  one  turn, 
rigidly  fastened  to  D.  C  is  provided  with  a 
handle.  D  and  0  are,  of  course,  movable  in  the 
bearings  F,  and  can  be  placed  in  anj»position  in 
the  arc  of  A.  Now  when  C  is  turned  until  directly 
opposite  B,  it  is  obvious  that  the  lines  of  force  set 
up  by  the  current  in  B  will  not  pass  around  A, 
but  will  take  a  short  cut  across  through  D,  and 
thus  round  and  round,  for  lines  of  magnetic  force, 
like  electricity,  always  take  the  path  of  least 
resistance.  Since  the  lines  of  force  do  this,  C,  in 
its  present  position  does  not  come  within  their  in- 
fluence, and  remains  inactive.  Thus  the  current 


THA.NSFOKMERS. 


in  B  reacts  solely  upon  itself,  and  by  self-induction, 
as  already  explained,  chokes  down  the  flow  of  cur- 
rent, and  the  lamps  in  its  circuit  glow  very  dimly. 
As  C  is  drawn  over  towards  B,  it  begins  to  en- 
close more  of  the  lines  of  force,  whereupon  cur- 
rent begins  to  flow  in  it,  and  it  becomes  a  sec- 
ondary. The  secondary  current  in  C,  reacts  upon 
B,  by  "  mutual  induction,"  and  permits  more  cur- 
rent to  flow,  the  lamps  becoming  brighter.  The 
nearer  to  B,  C  is  drawn,  the  more  lines  it  encloses, 
the  more  current  is  set  up  in  it,  and  the  more  it 
reacts  on  B,  till  when  C  rests  directly  over  JB,  all 
of  the  lines  of  force  are  brought  into  play,  the 
action  and  reaction  of  mutual,  and  self-induc- 
tion about  balance,  and  practically  full  current 
flows  through  B  to  the  lamps. 

We  have  now  to  consider  the  various  causes  of 
loss,  incident  to  the  transfer  of  energy,  from  the 
primary  to  the  secondary  of  a  transformer.  First, 
and  most  serious  is  the  C2R  loss  in  the  primary 
and  secondary.  This  is  dependent  solely  upon  the 
Ohms  resistance  of  the  two  coils,  and  is  in  accord- 
ance with  Ohms  law  with  which  we  assume  the 
reader  to  be  familiar.  This  loss  is  unavoidable, 
but  may  be  kept  at  a  minimum  by  using  as  few 
turns  as  possible  to  accomplish  a  given  result,  and 
by  using  copper  of  great  purity,  and  of  ample  sec- 
tional area  to  carry  the  required  current.  The 


THEORETIC   CONSIDERATIONS. 


47 


FIG.  14. 


4S  TRANSFORMERS. 

OR  loss  may  be  computed  by  means  of  Ohrns 
law.  after  measuring  the  Resistance  (in  Ohms)  of 
primary  and  secondary  coils. 

The  next  important  loss  in  the  transformer  is 
due  to  Eddy  or  Foucault  currents,  which  occur  in 
the  iron,  and  to  some  extent  in  the  coils  them- 
selves. As  has  been  stated  in  the  foregoing 
chapter,  the  character  of  these  currents  is  pretty 
clearly  emphasized  by  their  name.  They  are  very 
similar  in  character  to  the  local  eddies  and  currents 
which  are  to  be  found  everywhere  in  running 
streams  of  water.  The  iron  of  transformer  cores 
being  of  course  conductive,  current  in  the  primary 
coil  has  an  inductive  effect  upon  it,  quite  apart 
and  distinct  from  its  magnetising  influence ;  this 
effect  is  quite  analagous  in  character  to  the 
induction  of  current  in  the  secondary,  small  local 
currents  of  electricity  being  set  up  throughout  the 
mass  of  iron.  Energy  is  naturally  required  to 
generate  these  Eddy  currents,  and  this  energy  is 
taken  from  the  primary  and  secondary  circuits, 
which  induce  them,  whilst  as  these  Foucault  cur- 
rents do  no  useful  work,  the  force  expended  in 
generating  them  is  absolutely  wasted.  If  steps 
were  not  taken  to  prevent  the  presence  of  Eddy 
ciirrents  in  the  core,  in  dangerous  quantities,  they 
would  at  once  prove  disastrous  to  the  efficient 
operation  of  the  transformer;  this  would  be  the 
case  if  the  iron  were  one  solid  mass,  for  they  would 


TIIEOHKTIC    COXSIDEUATIOXS. 


4!) 


then  have  a  free  path  through  which  to  circulate. 
Fortunately  it  is  a  comparatively  easy  matter  to 
guard  against  and  prevent  the  generation  of  Eddy 
currents  in  dangerous  quantities  by  simply  so  sub- 
dividing the  core  that  the  path  through  which 
these  eddys  would  natually  flow,  is  broken  at 
short  intervals  by  minute  non-conductive  spaces,  or 
spaces  filled  with  matter  of  very  high  electrical 


25. 


resistance.  Since  the  potential  of  Foucault  cur- 
rents is  always  very  low,  these  insulating  spaces 
may  be  comparatively  imperfect. 

Since  Foucault  currents  must  always  have  a 
direction  consistently  in  the  plane  of  direction  of 
the  inducing  current ;  and  since  the  magnetic 
circuit  follows  a  direction  at  right-angles  to  the 
electric  circuit,  it  is  only  necessary  to  build  up  the 
iron  core  of  thin  sheets,  or  of  a  large  number  of  turns 
of  iron  wire  partially  insulated  from  one  another 
by  tissue  paper,  corrosion,  or  other  means,  to 


50  TRANSFORMERS. 

effectually  prevent  the  presence  of  Eddy  currents 
in  dangerous  quantities,  without  breaking  or 
interrupting  the  path  of  the  lines  of  force.  This 
may  be  better  understood  by  referring  to  Fig.  15, 
A  being  a  coil  of  wire  carrying  an  alternating 
current,  and  wound  around  an  iron  ring,  B.  The 
arrows,  (7,  indicate  the  plane  of  direction  of 
Foucault  currents,  whilst  the  arrows,  -D,  show  the 
plane  of  direction  of  the  magnetic  circuit.  The 
iron  ring  is  made  up  of  a  number  of  punched 
washer-like  pieces  of  sheet  iron,  separated  by  tissue 
paper  or  other  means,  and  closely  clamped  together. 
It  will  be  seen  that  the  path  of  the  Eddy  currents 
is  obstructed  at  short  intervals  by  the  layers  of 
insulation,  whilst  the  path  of  the  magnetic  lines 
is  closed  and  unobstructed.  The  same  would  hold 
good  if  the  core  was  constructed  of  a  bundle  or 
coil  of  iron  wire,  and  such  a  core  was  quite  largely 
used  in  early  practice,  but  a  laminated  core  of 
sheet  iron  is  now  almost  universal,  because,  aside 
from  economy,  the  magnetic  discontinuity  of  a 
closed  circuit  wire  core  is  obvious,  besides  which, 
plates  or  punchings  are  much  more  readily 
clamped  firmly  together. 

Practically  all  of  the  energy  which  is  present 
in  the  core  in  the  shape  of  Foucault  currents,  is 
expended  in  heating  the  iron ;  this  heat  is  objec- 
tionable, since  it  warms  the  copper  wire  of  primary 
and  secondary,  and  since  the  resistance  of  copper 


TIIEOUETIC   CONSIDERATIONS.  51 

increases  with  the  rise  of  temperature,  the  C2R 
loss  is  magnified,  and  it  becomes  necessary  to  use 
somewhat  larger  wire  than  would  be  required  if 
there  were  no  heating. 

Minute  Eddy  currents  are  also  induced  within 
the  copper  of  primary  and  secondary,  being  quite 
distinct  from  the  prime  currents,  but,  except  in 
transformers,  having  secondaries  of  large  current 
capacity  and  containing  therefore,  considerable 
masses  of  solid  copper,  their  influence  is  almost 
negligable,  tending,  however,  to  increase  the  tem- 
perature of  the  coils.  There  are  several  excellent 
formulae  for  computing  the  losses  due  to  Foucault 
currents.  Being  somewhat  complicated  and  in- 
volved, however,  they  have  been  omitted.* 

Foucault  current  losses,  in  combination  with 
other  heating  effects,  may  be  closely  and  easily 
computed  by  means  of  the  calorimeter,  which  will 
receive  further  mention  a  few  pages  later.  It  is 
obvious  that,  in  view  of  the  prejudicial  effect  of 
heat,  due  allowance  should  always  be  made  for  it, 
and  such  opportunity  for  radiation  be  provided  as 
is  consistent  with  mechanical  construction. 

Hysteresis,  the  last  of  the  loss  producing  forces 
to  be  considered,  is  far  less  clearly  defined  in 
character,  and  much  more  difficult  to  grasp,  than 
any  of  the  effects  as  yet  treated  of.  It  is  only 

*  For  an  able  theoretic  treatise  on  Eddy  currents,  we  would  refer 
the  reader  to  the  Phil.  Mag.,  (  England )  Jan.  and  Feb.  1884. 


52  TRANSFORMERS. 

very  recently  that  hysteresis  has  been  individual- 
ized and  separated  from  other  influences  of  similar 
effect. 

Hysteresis  may  probably  justly  be  considered 
as  being  the  direct  outcome  of  magnetic  inertia. 
Loss  by  hysteresis  may,  in  fact,  be  looked  upon  as 
the  energy  used  in  overcoming  a  kind  of  internal 
friction  between  the  molecules  of  iron,  which, 
according  to  the  accepted  theory,  change  their 
position  every  time  the  polarity  of  the  iron  is 
reversed,  and  this  theory  may  the  more  readily  be 
accepted,  since  the  loss  due  to  hysteresis  decreases 
with  the  increase  of  mechanical  vibration,  which 
serves  to  agitate,  and  therefore  assists  in  moving 
the  molecules.  Let  us  suppose  a  piece  of  iron  to 
be  so  enormously  magnified  that  the  eye  can 
distinguish  the  molecules,  one  from  another,  the 
whole  mass  having  the  appearance  of  an  enormous 
number  of  particles  grouped  together  and  held  in 
the  form  of  a  homogeneous  mass  only  by  molecular 
attraction,  as  is  really  the  case.  When  this  mass 
is  subjected  to  the  influence  of  an  electric  current, 
it  becomes  magnetically  polarised,  that  is,  each 
molecule  has  a  north  and  a  south  pole.  Now  if  the 
current  be  reversed  in  direction,  the  magnetism 
necessarily  reverses,  not,  as  it  might  seem,  by  the 
molecules  being  first  demagnetized  and  then  mag- 
netized in  an  opposite  direction,  but  by  turning  all 
of  the  molecules  half-way  round,  so  that  their  ex- 


THEORETIC  CONSIDERATIONS.  53 

isting  poles  may  coincide  with  the  reversed  con- 
ditions.* This  reversal  is  necessarily  accomplished 
by  the  expenditure  of  a  certain  amount  of  energy, 
which  results  directly  in  heat,  due  (  we  assume ) 
to  molecular  friction.  This  waste  of  energy,  is  the 
loss  due  to  hysteresis.  Hysteresis  losses  naturally 
increase  with  the  frequency  of  the  alternations, 
and  almost  in  a  direct  ratio. 

The  heat  losses  due  to  Foucault  currents,  and 
to  hysteresis,  can  most  conveniently  be  ascertained 
by  the  Calorimeter  test.  The  principle  of  this 
method  is  simply  the  measurement  of  the  rise  in 
temperature  due  to  these  effects,  whose  value  is 
then  established  by  comparison  with  a  scale  of 
temperatures  due  to  known  expenditures  of  energy. 
The  transformer,  or  other  piece  of  apparatus  in 
which  these  losses  are  to  be  measured,  is  placed 
within  a  closed  box,  whose  temperature  is  normally 
fixed,  owing  to  its  being  packed  in  ice,  or  sur- 
rounded by  circulating  water  or  air.  The  total 
rise  in  temperature  above  normal,  of  the  air  within 
the  box,  then  represents  the  total  heat  losses. 

This  method,  which  is  extremely  exact,  is  not 
more  fully  described,  as  it  is  commonly  used  in  the 
most  careful  and  exact  tests,  as  carried  out  in  the 
leading  technical  schools. 

*  It  must  be  borne  in  mind  that  we  are  treating  of  a  theory,  which  is 
however,  generally  accepted. 


54  TRANSFORMERS. 

The  commoner  method  (though  less  exact)  is  to 
measure  the  total  losses,  by  simply  ascertaining  the 
watts  expended  in  the  primary,  when  the  second- 
ary is  idle,  due  allowance  being  made  for  magnet- 
ism and  C2R  losses.  The  per  cent  of  loss  (at  full 
load)  in  the  average  transformer  of  today  varies 
from  about  10  to  15  per  cent  in  very  small,  to  3  to 
5  per  cent  in  large  converters.  It  is  probably 
easier  to  design  a  transformer  of,  say  10,000  watts 
capacity,  with  an  efficiency  of  about  97.5  per  cent, 
than  a  250  watt  converter,  with  an  efficiency  of  90 
per  cent.  For  this  reason  the  fewer  the  number 
and  the  greater  the  size  of  the  transformers,  for 
a  given  number  of  lights,  the  greater  the  efficiency 
of  the  system,  provided,  always,  that  the  converters 
are  working  at  full  load  in  both  cases.  A  con- 
verter is,  of  course,  most  efficient  at  full  load,  for 
the  waste  (except  the  C2R  losses)  is  practically  a 
fixed  quantity  at  all  loads.  For  this  reason  trans- 
formers should  not  be  installed,  having  a  capacity 
in  excess  of  what  they  are  called  upon  to  supply. 
Further  information  relative  to  this  will  be  found 
in  chapter  VI. 

The  reader  may  note  that  the  question  of  lag 
has  been  neglected.  This  has  been  done  intention- 
ally, and  after  due  consideration,  as  purely  techni- 
cal matters  do  not  seem  to  be  in  keeping  with  the 
character  of  the  work  in  hand. 


MATHEMATICAL   CONSIDERATIONS.  55 

. 

'// 


CHAPTER  III. 

THE  THEORY  OF  THE  TRANSFORMER   MATHEMATI- 
CALLY   CONSIDERED. 

WHILST  it  has  been  deemed  advisable  to  avoid, 
as  far  as  possible,  all  purely  technical  matters  in 
this  work,  it  could  scarcely  be  considered  complete 
without  at  least  a  brief  consideration  of  the  math- 
ematical theory  of  the  converter.  After  due  con- 
sideration Hopkinson's  Formulae  for  the  Trans- 
former, as  set  forth  by  Prof.  S.  P.  Thompson,  has 
been  selected,  as  being  at  once  the  simplest  and 
the  most  direct. 

The  following  equations  are  not,  in  the  remotest 
sense,  original  in  any  respect.  They  are  presented 
purely  for  the  convenience  of  the  reader,  and  in 
the  simplest  form  possible.  A  knowledge  of  alge- 
bra only  is  presumed. 

The  following  symbols  have  been  assumed: 
A — Sectional  area  of  core  in  square  centimeters. 
EI — The   whole   applied   electro- motive    force    in 

primary. 

C — Current  in  amperes  in  external  circuit. 
Ci — Current  (absolute  C.  G.  S.  units)  in  primary,- 


56  TRANSFORMERS. 

C2 — Current  (absolute  C.  G.  S.  units)  in  secondary. 
H — Intensity  of  magnetic  field. 
L! — Coefficient  of  self-induction  in  primary  coil. 
L2 — Coefficient  of  self-induction  in  secondary  coil. 
1 — Length  of  magnetic  circuit  in  core. 
M — Number  of  magnetic  lines  per  square  centi- 
meter.    The  magnetic  induction. 
N — Total  number  of  lines  of  force  traversing  the 

core, 
p — Coefficient  of   transformation — ratio   between 

windings. 

R — Resistance  of  external  circuit  in  ohms. 
Ri — Resistance  of  primary  in  ohms. 
R2 — Resistance  of  secondary  in  ohms. 
r2 — Internal  resistance  of  secondary  in  ohms. 
Si — Number  of  turns  of  wire  in  primary  coil. 
S2 — Number  of  turns  of  wire  in  secondary  coil. 
t — Time  measured  in  seconds. 
p — Coefficient  of  magnetic  permeability  of  iron. 

It  is,  of  course,  understood  by  the  reader  that  IT 
is  the  accepted  symbol  for  the  ratio  of  the  circum- 
ference to  the  diameter  of  a  circle,  which  equals 
about  272  of  the  diameter;  or,  more  exactly,  3.14195.* 
Hopkinson's  theory  of  the  transformer  has,  as  its 
basis,  the  magneto-motive  forces;  or,  to  state  it 
more  clearly,  the  applied  magnetism-creating 
energy  at  work  in  the  iron  core.  Considered  as 

*  It  is  well  to  remember  the  following  expressions :    Circumference 
of  a  circle  =  2jrr.    Area  of  a  circle  =  rrr3.    r,  denoting  the  radius. 


MATHEMATICAL  CONSIDERATIONS.  57 

resulting  from  the  algebraic  sum  of  the  ampere 
turns  in  the  primary  and  secondary,  from  this  the 
voltages  resulting  from  the  variations  in  the  mag- 
netic induction  of  the  core,  are  deducted. 

Hopkinson  first  considers  the  magneto-motive 
force  necessary  to  project  N  lines  of  force  through 
a  core,  having  1  length  and  ^  permeability  —  this, 
of  course,  being  entirely  dependent  on  the  quality 
of  the  iron.  The  total  number  of  magnetic  lines 

__  magneto-motive  forces. 
magnetic  resistance. 

or  we  may,  according  to  Hopkinson's  formulae, 
write  : 


If  we  know  the  cross  sectional  area  of  the  iron 
(A),  and  the  number  of  lines  per  square  centimeter 
(B),  we  may  say: 

N=AB     (,) 

in  which  case  the  magneto-motive  force  is 


Next  state  two  equations  for  the  pressures 
created  in  the  primary  and  secondary  circuits,  as 
follows  : 


0=(r2+R2)i2-S2f  =(r,  +Ra)i— S,A*g     (5) 


58  TRANSFORMERS. 

.  K2  being  the  resistance  of  the  lamp  circuit  and 
.r2  the  resistance  of  the  secondary  coil  itself.  We 
now  multiply  the  fourth  equation  by  S2  and  the 
fifth  by  Si,  getting : 

S,E1=S,Rlii-^3i(r,+R1)i,     (•) 
this,  with  the  third  equation,  gives  us : 

it  j  SiR!+S?(r2+R2) }  =S*E1-}-S1(r2+R2)(10Hl-M7r) 

i,{SSRi+Sf(r,+R,)}=—  SiS-, 

and 

AdB _   (r,+B,)S1E1      J_  10H1 

Adt —      S|R1+Stfrt+Bi'~T  4,    ' 

The  second  term  (8)  may  be  ignored,  since  HI 
is  insignificant  in  comparison  with  jjj^ii ;  it  being 
only  the  difference  between  Siii  and  S2i2  (which 
are  large  factors),  that  is  needed  as  a  magneto- 
motive force,  which  is  small,  provided  the  permea- 
bility of  the  iron  is  great  as  is  customary  in  actual 
practice.* 

We  have,  therefore : 

AdB dN (ra+RJ)S1E,          (  -\ 

•""dt       dt  S}R,+SKra+Rs)      ^ 

bearing  in  rnind  that : 

^F^ffjg     (10) 

*It  is  not  generally  customary  to  carry  the  number  of  lines  much 
above  10,000  lines  per  square  centimetre. 


MATHEMATICAL   CONSIDERATIONS.  59 

we  have : 


Since  the  effective  electro-motive  force  in  the 
secondary  circuit  (E2)  is  equal  to  (r2-{-R2)i2,  it 
follows'that : 

Eigf         GO 

g^+r.+R,    ' 

Assuming  (as  is  practically  true)  that  the 
voltage  at  the  terminals  of  the  primary  coil  of  the 
transformer  is  constant,  we  may  take  E.  and  .R.,  as 
relating  purely  to  that  which  is  internal  in  the 
primary  coil ;  and  it  is  quite  plain  that  the  action 
of  the  converter  is  to  reduce  (or  increase)  the 
pressure  in  direct  proportion  to  the  ratio  of  the 
winding,  for  example,  to  reduce  a  primary  pressure 
of  1,000  volts  to  a  secondary  E.  M.  F.  of  50  volts 
we  might^say,  50  :  1,000  : :  100  :  x  or  2,000  turns  of 
primary^to  100  turns  secondary,  or  20  to  1,  follow- 
ing a  like  argument  in  all  required  secondary  volt- 
ages. We  also  see  from  the  foregoing  arguments 
that  the  effect  of  the  transformer  is  to  add  to  the 
resistance  of  the  secondary  circuit  a  term  equal  to 
the  resistance  of  the  primary,  reduced  in  proportion 
to  the  square  of  the  ratio  of  the  windings.  It  is 
also  obvious  that,  owing  to  the  negative  sign  in 


60 


TRANSFORMERS. 


equation  number  twelve,  the  two  currents  are  in 
exactly  opposite  phases. 

It  is  a  general,  and  a  pretty  safe,  rule  to  assume 
that  the  weight  of  copper  in  primary  and  in 
secondary  are  equal,  this  being  so  the  following 
table  of  relations  and  proportions  will  be  found  to 
be  correct.  We  quote  this  table  from  "Dynamo 
Electric  Machinery  "  by  Prof.  S.  P.  Thompson. 


PRIMARY. 

SECONDARY. 

RATIO. 

Windings  

8, 

S2 

P 

Kesistance  .... 

TI 

r2 

P2 

Self-induction.    .    . 

L, 

L2 

P2 

E.  M.  F  

E, 

E2 

P2 

Current  

ij 

is 

P 

Heat  Waste.    .    .    . 

il'ri 

i22r2 

1 

As  has  been  seen,  the  question  of  proportioning 
the  iron,  depends  almost  absolutely  on  its  perme- 
ability, and  the  length  of  the  magnetic  circuit,  the 
following  weight,  however,  is  a  fair  average  for  the 
various  medium  sizes  of  standard  commercial 
transformers.*  Weight,  per  useful  applied  watt  at 
secondary  terminals  equals  .103  Ibs.  This  includes 
weight  of  copper,  etc.,  which  must  be  deducted  to 
get  iron  weight  where  required.  Very  small  trans- 
formers are  heavier  in  proportion,  whilst  very 
large  ones  are  generally  much  lighter. 

*  15  to  30  lights. 


MATHEMATICAL   CONSIDERATIONS. 


61 


A 

0 
0 

v 

0) 
CO 

H 
0 

A, 

3 

_A^ 

1 

s 

^ 

^ 

o 

X 

\ 

\ 

V 

^ 

^  — 

— 

9 

• 

— 

«s 

(, 

Ll 

? 

s 

i 

Vj 

=? 

62  TRANSFORMERS. 

It  is  of  course,  understood  that  the  efficiency  of 
a  transformer  vanes  "With  the""loat!r'the  least 
efficient  point  being  the  lowest  load,  and  the  most 
efficient,  the  highest.  TKe  efficiency  is  graphically 
shown  by  plotting  the  results  _of  tests  as  an 
efficiency  curve.  A  good  example  of  this  is  shown 
at  Fig.  16. 

The  horizontal  lines  representing  the  per  cent  of 
efficiency,  and—  the.  verticals-lines,  the  load  in 
thousands  of  watts.  In  this  particular  case  it  will 
be  noted  that  -the- maximum  efficiency  shown  is 
97  per  cent,  the  remaining  3  per  cent  representing 
the  losses.  The  potential  of  the  secondary  also 
varies  somewhat  with  the  load,  it  being  highest  on 
very  low  loads,  and  lowest  on  full  loads.  The 
average  variation  between  one  lamp  and  full  load, 
being  about  1.9  volts,  in  average  sizes  of  conver- 
ter. 


EVOLUTION   OF   TKAXSFOKMEIi. 


CHAPTER  IV. 

EVOLUTION    OF    THE   ELECTRICAL   TRANSFORMER. 

IN  these  clays  the  alternating  system  has  come 
into  universal  use.  The  high  potential  current  of 
the  dynamo  is  carried  great  distances  with  but 
little  loss,  and  is  reduced  to  the  low  pressuie 
necessary  for  house  lighting,  by  means  of  a  trans- 
former— one  of  a  dozen  or  more  kinds — all  of  them 
efficient,  sure  in  their  action,  and  entirely  reliable. 
Transformers  are  sold  as  a  mere  commercial  article, 
and  lighting  companies  order  a  dozen  of  them  as  a 
cook  might  a  dozen  eggs. 

In  view  of  all  these'  facts,  it  is,  perhaps  but 
natural  in  us  to  forget  that  the  success  of  the 
transformer,  in  fact  the  discovery  of  its  principles, 
is  a  matter  of  comparatively  recent  date,  and  that 
it  has  gone  through  very  many  changes  •  before 
reaching  its  present  comparatively  perfect  form. 
Many  people,  if  asked  who  first  invented  and  used 
the  induction  -coil,  would  answer,  if  they  were  only 
casual  readers  on  the  subject — "Ruhmkorff."  It  is 
very  easy  for  us  in  these  days  to  forget  Faraday 
and  his  discoveries.  Still  easier  to  forget  that  the 
origination  of  the  transformer  is  due  to  him.  Yet 


64  TRANSFORMERS. 

the  original  transformer  of  Faraday  embraced  all 
of  the  essential  features  of  the  best  transformers 
of  today. 

Fig.  17,  represents  the  original  "Perfected  In- 
duction Coil"  of  Faraday.    A  is  a  ring  of  cast-iron, 


B 


FIG.  17. 


B  the  secondary,  C  the  primary.  It  will  readily 
be  seen  that  we  have  here  the  most  essential 
feature  of  the  modern  transformer,  namely, — a 
closed  magnetic  circuit. 

The  Ruhmkorff  induction  coil  was  invented  and 
patented  in  1842  (see  Fig.  18  ). 

Its  construction  is  familiar  to  all — a  straight  rod 
of  iron  forming  a  core,  a  primary  wound  upon  it, 
and  a  secondary  upon  that. 

This  coil  was  designed,  and  is  very  extensively 
used  for  inducing  high  from  low  potential  inter- 


EVOLUTION   OF   TRANSFORMER.  65 

mittent  or  interrupted  currents,  in  connection  with 
batteries,  in  laboratory  work,  and  also  for  medical 
and  electro-chemical  purposes. 

The  Faraday  and  Ruhmkorff  coils,  are  types  of 
the  two  classes  of  converter  prevailing  today — the 
opened  and  the  closed  circuit  transformers.  It 
will  readily  be  seen  however  that  the  Ruhmkorff, 
having  a  straight  core,  must  complete  its  energetic 
circuit  through  the  air ;  thus  its  magnetic  circuit 
is  of  high  resistance  and  presents  a  strong  contrast 
to  the  Faraday  coil,  which  has  a  complete  mag- 


FIG.  18. 

netic  circuit  of  iron,  and  hence  of  low  resistance. 
Generally  speaking,  the  lower  the  resistance  of  the 
magnetic  circuit,  the  greater  the  efficiency  of  the 
transformer,  provided  other  parts  are  properly 
proportioned.  The  converters  of  the  Faraday  type 
are  therefore  the  more  efficient,  and  the  trans- 
former of  today  is  almost  universally  of  this  class. 
To  shorten  and  lower  the  resistance  of  the  mag- 
netic circuit  is  one  of  the  chief  aims  of  the  modern 


66  TKAJJSFOKMEKS.- 

transformer  builder.  This  is  done  in  four  ways; 
first,  by.  making  the  circuits  entirely  of  iron  ; 
second,  by  shortening  these  magnetic  circuits  as 
much  as  possible ;  third,  by  increasing  the  sec- 
tional area  as  much  as  is  consistent  with  weight ; 
and  fourth,  by  using  iron  of  the  greatest  magnetic 
permeability.  With  these  features  always  in  view, 
and  due  care  with  regard  to  insulation,  and  the 
best  ventilation  possible,  a  transformer  with  prop- 
erly proportioned  windings,  can  be  made  extremely 
efficient.  It  is  interesting  to  note  the  various 
changes  and  improvements  which  the  transformer 
has  passed  through  in  attaining  its  present  high 
character. 

Jablochkoff  and  Goulard  &  Gibbs,  used  trans- 
formers of  the  Ruhmkorff  type  in  the  first  distri- 
bution which  was  attempted  by  the  alternating 
system.  These  early  transformers  were  used  in 
series,  a  practice  which  has  long  since  been  discon- 
tinued except  in  connection  with  one  or  two 
systems  of  street  lighting,  and  for  special  pur- 
poses. Probably  the  first  improvement  on  the  old 
Faraday  coil  (and  it  was  a  very  slight  one),  was 
made  by  Kennedy  in  '83 ;  he  employed  the  same 
large  iron  ring,  with  alternate  windings  of  primary 
and  secondary,  the  improvement  being  in  the  ring, 
which  was  of  iron  wire  instead  of  cast-iron,  thus 
gaining  greater  magnetic  permeability,  it  being 
wrought,  iron  highly  laminated.  Ferranti  some- 


EVOLUTION  OF  TRANSFORMER.  67 

what  improved  this  a  little  later,  by  winding  strip 
iron  around  the  periphery  over  the  coils.  This 
somewhat  reduced  the  magnetic  resistance,  since 
it  increased  the  cross-section  of  iron  employed ;  it 
also  served  to  inclose  any  magnetic  leakage  which 
might  occur.  The  merits  of  this  device  were 
questionable  however,  the  additional  iron  neces- 
sarily increased  the  weight,  whilst  the  ventilation 


FIG.  18  A. 

being  reduced,  heating  naturally  resulted,  and  the 
liability  of  a  "burn  out"  increased. 

Stanley  a  little  later  made  a  transformer,  which 
he  claimed  to  be  a  marked  improvement  over  any- 
thing then  existing.  He  made  a  ring  of  finely 
laminated  iron  of  the  shape  shown  in  Fig.  18  A, 


68  TRANSFORMERS. 

This  was  an  adoption  of  the  Paccinotti  ring  arma- 
ture. It  is  difficult  to  say  what  were  the  advantages 
expected  to  result  from  this  construction.  The 
leakage  from  the  teeth  of  the  ring  was  anything 
but  desirable,  a  considerable  amount  of  magnetic 
energy  doubtless  being  thus  dissipated.  It  how- 
ever served  to  give  an  idea  to  Dick  and  Kennedy, 


FIG.  is  B. 

who  in  '86  introduced  a  transformer  which  showed 
the  first  really  vital  improvements  since  the  days 
of  Faraday. 

Starting  with  Stanley's  Paccinotti  ring,  they 
wound  the  periphery  with  thin  sheet  iron,  the 
result  being  a  transformer  in  appearance  like  Fig. 
18  B.  A  coil  of  considerable  efficiency  and  correct 


EVOLUTION   OF   TRANSFORMER. 


principle.  Much  of  the  efficiency  which  should 
have  been  gained  by  the  reduction  of  the  length 
of  the  magnetic  circuits,  was  sacrificed  by  the 
magnetic  resistance  due  to  these  circuits  not  fol- 
lowing the  direction  of  the  lamination  in  the 
peripheral  iron. 

But  at  this  point  in  the  history  of  the  transfor- 
mer, the  question  of  cost  began  to  demand  serious 
attention.  Up  to  this  time  all  of  the  closed  cir- 
cuit transformers  had  hand  wound  coils.  The 
shape  of  the  iron  punchings  made  them  wasteful 
and  expensive.  The  iron  on  the  periphery  was 
difficult  to  wind,  and  any  repairs  necessitated 
tearing  the  whole  thing  to  pieces.  But  though  too 
expensive  for  commercial  use,  the  Dick  and  Ken- 
nedy transformer  of  '86,  was  in  some  respects 
excellent  in  principle.  The  magnetic  core  was 
cut  up  into  a  number  of  short  circuits  of  theoreti- 
cally low  resistance,  as  indicated  by  the  arrows  in 
Fig.  18  B.  The  magnetic  lines  of  force  were  quite 
well  enclosed,  opportunities  for  magnetic  leakage 
being  almost  entirely  absent,  and  the  ventilation 
was  good.  A  number  of  tests  of  this  transformer 
carefully  conducted,  proved  its  efficiency  to  be 
fairly  high.  There  is  a  further  objection  to  this 
coil  however,  which  applies  equally  to  all  of  the 
early  ring-shaped  transformers.  The  space  occu- 
pied was  quite  disproportionate  to  the  work  done. 
This,  together  with  the  difficulty  and  expense  of 


70  TRANSFORMERS. 

winding,  eventually  led  to  the  abandonment  of  the 
ring  transformer  in  its  original  form  of  an  endless 
jointless  iron  ring. 

One  of  the  best,  perhaps  the  very  best,  of  the 
early  ring-shaped  transformers  was  presented  to 
the  public  in  1885,  by  Messrs.  Zipernowski  and 
Deri.  In  this  transformer,  which  electrically  was 
excellent,  but  mechanically  very  faulty,  the  posi- 
tions of  coils  and  iron  were,  so  to  speak,  reversed. 
The  primary  and  secondary  coils,  both  thoroughly 
insulated  being  wound  into  a  kind  of  solid  core, 
which  was  over-wound  with  a  heavy  layer  of  iron 
wire.  Owing  to  the  shortness  and  abundant  sec- 
tional area  of  the  magnetic  circuit,  this  transfor- 
mer had  excellent  self-regulation,  and  owing  to 
the  large  radiating  surface  of  the  iron,  the  heating 
effect  was  considerably  reduced.  Mechanically, 
the  construction  was  obviously  „  open  to  many 
objections. 

About  the  date  of  the  perfecting  of  the  Ziper- 
nowski &  Deri  transformer,  the  more  modern 
"block  shaped"  class  of  converter  commenced  to 
attract  attention. 

These  transformers  are  of  many  kinds,  no  one 
differing  very  essentially  from  another  except  in 
details  of  construction,  proportioning,  efficiency 
and  workmanship.  This  class  of  transformers 
generally  has  the  coils  and  iron  arranged  about 
as  shown  in  the  accompanying  drawing,  Fig.  18  C. 


EVOLUTION   OF   TRANSFORMER. 


71 


Thus  the  coils  are  entirely  surrounded  by  lami- 
nated iron  save  at  their  ends,  whilst  the  magnetic 
circuits  are  comparatively  short  and  in  two  direc- 
tions, the  whole  apparatus  being  mechanically 
simple,  and  easy  to  assemble. 

Block  transformers  are  those  chiefly  in  use  at 
the  present  day,  and  whilst  the  various  makes 
vary  in  detail,  their  general  plan  is  similar.  The 
efficiency  of  the  modern  transformer  is  very  high, 


\  / 


FIG.  18  C. 

and  its  regulation  is  admirable.  It  may  be 
taken  as  an  unquestionable  fact  that  more  light 
is  being  distributed  today  by  means  of  the  conver- 
ter than  by  all  of  the  direct  current  systems  com- 
bfnecT  There  are  still  some  strong  supporters  of 
the  open  magnetic  circuit  transformers  of  which 
the  "  Ruhmkorff  coil "  is  a  type,  and  by  careful 
construction  and  proportioning,  some  remarkable 
results  have  been  obtained  from  time  to  time. 


72  TRANSFORMERS. 

A  notable  example  of  this  is  the  English  "  Hedge- 
hog "  transformer  of  Swinburne,  which  attracted 
so  much  attention  some  time  since.* 

As  a  class  however,  the  open  circuit  trans- 
formers from  their  very  principle  never  have  and 
never  can  become  generally  successful.  There 
are  one  or  two  transformers  now  in  use  of  rather 
unique  design,  which  show  no  especial  feature  of 
excellence,  and  which  form  no  link  in  the  chain  of 
improvement  which  we  have  attempted  to  follow, 
but  which  are  none  the  less  reliable  and  efficient, 
though  perhaps  less  so  than  others  of  the  present 
day.  A  good  example  of  these  is  the  Ferranti 
converter,  which  is  referred  to  elsewhere. 

The  chief  direction  of  improvement  in  transfor- 
mer construction  today,  tends  first,  toward  greater 
efficiency,  and  secondly  toward  the  bettering  and 
simplifying  of  case  and  fixtures,  such  as  fusing 
devices. 

Whilst  we  can  scarcely  look  for  the  105  per  cent 
efficiency,  which  some  printed  matter  has  now  and 
then  seemed  to  hint  at,  still  the  transformer,  of 
1892  has  crept  up  very  close  indeed  to  the  other 
side  of  the  100^. 

*  See  Appendix. 


TRANSFORMER   CONSTRUCTION.  73 


CHAPTER  V. 

TRANSFORMER   CONSTRUCTION. 

IN  considering  the  transformer  and  its  structure 
from  a  purely  mechanical  point  of  view,  the  student 
is  at  once  confronted  with  a  multitude  of  formsr 
each  possessing  its  own  especial  advantages.  Few 
it  must  be  confessed,  can  be  found,  which  do  not 
show  some  noticeable  defects.  In  preparing  this 
chapter  it  has  been  our  endeavor  to  classify  the 
different  steps  in  the  construction,  treating  them 
progressively,  rather  than  as  a  whole. 

The  general  character  of  the  transformer  is  at 
once  determined  by  the  form  of  core  employed, 
and  in  this  portion  of  the  apparatus,  good  mechani- 
cal construction,  probably  does  more  to  influence 
the  excellence  of  the  results  than  in  any  other 
portion  of  the  work 

On  pages  74-75  are  shown  some  typical  forms  of 
cores,  all  more  or  less  in  use  at  the  present  day. 

No.  1  is  without  doubt  the  most  typical  and 
characteristic  form  of  the  modern  transformer, 
the  "block-shaped"  converter  of  the  preceding 
chapter,  A  and  B  are  respectively,  the  iron  and  the 


74 


TRANSFORMERS. 


TRANSFORMER  CONSTRUCTION. 


no.  s. 


76  TRANSFORMERS. 

winding.  A  is  laminated,  in  the  direction  shown 
in  cut,  which  is  of  course,  a  section.  It  will  be 
noticed  at  once  that  the  coils  in  this  form  of  con- 
verter are  easy  to  wind  and  most  compact.  Some 
manufacturers  wind  the  primary  and  the  secondary 
into  two  coils  of  equal  internal  diameter,  placing 
them  upon  the  iron  side  by  side,  others  again  wind 
either  the  primary  or  secondary  of  greater  internal 
circumference  so  that  the  one  may  fit  snugly  over 
the  other ;  whilst  in  some  instances  the  two  •  are 
combined  in  one  solid  mass.  In  this  latter  case 
the  primary  or  secondary  is  first  wound  upon  the 
mandril  and  completed,  this  then  in  its  turn,  is 
overwound  with  due  insulation,  upon  which  is 
placed  the  second  coil,  the  secondary  generally 
forming  the  outer  layer.  It  is  obvious  that  in  this 
form  of  converter,  the  iron  must  be  divided  at 
some  point  to  permit  of  the  introduction  of  the 
coils. 

Very  many  different  methods  have  been,  and, 
in  fact,  are  still,  in  use  for  joining  the  iron,  the 
object,  in  all  cases,  being  to  obtain  as  good  a 
contact  as  possible  between  the  abutting  ends,  and 
thus  avoid  the  introduction  of  unwarranted  mag- 
netic resistance  resulting  from  a  gap  or  break  in 
the  path  of  the  lines  of  magnetic  force.  Some 
manufacturers  prefer  to  break  each  plate  of  the 
lamination  at  the  same  line,  thus  permitting  the 
two  blocks  formed  by  clamping  the  plates 


TRANSFORMER  CONSTRUCTION.  77 

together,  to  abut  as  two  solid  masses,  whilst  others 
break  the  plates  at  alternate  lines,  thus  overlap- 
ping each  break  with  the  solid  portion  of  the 
next  sheet  above  it. 

A  clear  idea  of  what  is  meant  may  be  had  by 
glancing  at  cut  21.  In  the  latter  method  the 
iron  necessarily  has  to  be  built  up  within  the  coils, 
which  probably  renders  the  assembling  of  the 
transformer  somewhat  more  laborious.  In  either 
case  a  very  perfect  magnetic  joint  is  secured  by 
proper  care,  and  at  this  point  as  in  almost  every 


other  detail  of  construction,  care  in  the  manufac- 
ture bears  a  very  important  relation  to  the  final 
efficiency  obtained.  Cut  22  shows  some  of  the 
commoner  lines  at  which  the  cores  of  block-shaped 
transformers  are  broken.  In  transformers  of 
medium  and  large  size,  it  is  a  very  common  practice 
to  wind  several  coils,  each  of  primary  and  second- 
ary. 

Cut  2,  Fig.  19,  shows  us  another  form  of  trans- 
former in  use  at  the  present  day.     This  as  well 


78 


TRANSFORMERS. 


as  No.  8,  Fig.  20,  ( which  it  closely  resembles)  is  a 
ring-shaped  transformer,  having  the  iron  (which 
we  can  scarcely  term  a  core  in  this  case)  on  the 
outside.  In  transformers  of  this  type,  the  primary 
and  secondary  are  formed  into  a  solid  internal 
ring,  the  two  circuits  being  of  course  duly  separ- 
ated one  from  the  other.  Upon  this  ring  of  wire 
is  placed  the  iron.  In  the  case  of  type  8,  this  con- 


32. 


sists  of  iron  wire  overwound  upon  the  coils  by 
hand,  a  tedious  and  expensive  operation. 

This  form  of  construction  is  seldom,  if  ever  used. 
Commonly  the  iron  consists  of  sheets  or  plates,  as 
in  the  block  form,  and  as  before,  the  plates  have,  of 
course,  to  be  broken  at  some  line,  to  permit  of  the 
free  introduction  of  the  winding. 

This  form  of  transformer  presents  the  merit  of 
a  short  magnetic  circuit.  The  external  circum- 
ference of  the  ring  being  of  course  greater  than 
the  internal,  it  follows  (the  plates  of  iron  being  of 


TRANSFORMER  CONSTRUCTION.  79 

uniform  thickness)  that  the  peripheral  edges  of 
the  plates  must  be  somewhat  separated,  even 
though  the  inner  edges  be  clamped  very  closely 
together,  and  this  is  a  mechanical  difficulty  to  be 
overcome,  although  it  is  conclusive  to  very  perfect 
lamination. 

Cut  4,  Fig.  19,  shows  us  a  section  through  a 
transformer  of  rather  unique  construction.  The 
iron  in  this  case  consists  either  of  bundles  of  very 
thin  soft  hoop  iron  well  bound  together,  or,  in  a 
few  isolated  instances  of  soft  iron  wire.  A  num- 
ber of  bundles  of  this  iron  being  brought  together 
parallel,  and  in  the  same  plane,  they  are  overwound 
and  bound  together  by  insulation  at  their  central 
portion.  Over  this  insulation  is  wound  the 
secondary,  and  over  this  again  is  placed  the  pri- 
mary, generally  in  the  form  of  ready  wound  coils, 
due  insulation  being  interposed.  The  soft  iron  is 
then  turned  back  and  over  from  each  end,  the  ends 
of  the  strips  lapping  one  over  the  other,  till  the 
middle  of  the  bundle  is  reached,  when  the  last  two 
ends  are  turned  back  and  made  fast ;  the  remain- 
ing half  of  the  iron  is  then  turried  back  similarly 
in  the  opposite  direction,  the  iron,  when  in  posi- 
tion, enclosing  the  coils  as  in  the  block  trans- 
former. 

This  design  presents  some  merits,  chiefly 
mechanical,  probably  the  most  marked  being  the 
ease  with  which  injured  coils  may  be  removed  and 


80  TRANSFORMERS. 

replaced.  Where  iron  wire  is  used  for  the  core, 
the  device  differs  somewhat,  in  that  the  iron  is 
turned  back  around  the  coils  in  all  directions,  in- 
stead of  in  two  directions  only,  and  in  this  case,  as 
in  most  wire-cored  converters,  the  coils  are  gen- 
erally circular.  Wire-cored  transformers  of  this 
type  are,  however,  only  made  in  small  sizes  and 
for  especial  purposes.  As  a  type,  this  general  style 
of  converter  has  been  somewhat  popular  abroad, 
and  has  been  adapted  to  very  high  voltages,  large 
capacities,  and  step-up  purposes. 

No.  3,  Fig.  19,  shows  us  another  form  of  the 
popular  block-shaped  transformer.  It  will  be 
noticed  that  the  iron  only  encloses  one-half  of  the 
wire,  hence  the  converter  is,  generally  speaking, 
less  efficient  for  the  same  weight  of  iron  than  the 
usual  block  form.  Transformers  of  this  type  are 
used  solely  for  special  and  experimental  purposes. 
Its  only  merit  lies  in  its  extreme  simplicity. 

In  cut  7,  Fig.  20,  we  have  the  modern  form  of 
the  original  Faraday  "Perfected  Induction  Coil," 
a  typical  ring-shaped  converter.  The  iron  core  is 
of  wire,  wound  upon  a  form  and  bound  closely 
together  with  insulating  material,  which  serves  to 
isolate  it  from  the  coils.  The  primary  and  second- 
ary are  over-wound  upon  this,  necessitating  much 
hand  labor.  At  times  one-half  of  the  ring  is 
devoted  to  the  primary  winding  and  the  other  to 
the  secondary,  as  shown  in  the  illustration.  Some- 


TRANSFORMER  CONSTRUCTION.  81 

times  the  two  circuits  are  divided  into  a  number 
of  short  coils,  placed  alternately,  and  again  one 
coil  is  wound  over  the  other.  Transformers  of 
this  type  are  not  common  in  practice,  as  they 
present  numerous  disadvantages,  not  the  least  of 
which  is  in  construction.  They  have  been  used, 
however,  in  connection  with  series  lighting,  and 
for  special  converters  of  small  capacity. 

Types  of  the  open  circuit  transformer  are  shown 
in  Fig.  20,  Nos.  5  and  6.  The  core  is  almost  in- 
variably of  wire,  straight  and  non-continuous,  the 
magnetic  circuit  being  completed  through  the  air. 
No.  6  is  the  popular  form  of  the  early  Ruhmkorff 
coil,  already  mentioned  in  previous  chapters.  Its 
general  plan  of  construction  is  so  simple  as  to  need 
no  comment,  more  especially  as  it  bears  no  especial 
relation  to  electric  lighting,  although  in  the  early 
days  it  was  used  in  series  distribution.  The  same 
modifications  of  winding  are  used  in  this,  as  in  the 
ring  transformer  described  as  No.  7.  Although 
quite  typical  and  very  useful  for  many  purposes, 
transformers  of  this  class  may  safely  be  put  aside 
as  essentially  inefficient. 

Cut  No.  5  illustrates  the  general  plan  of  con- 
struction of  the  so-called  "  Hedgehog  "  transfor- 
mer. Notwithstanding  its  similarity  to  No.  6  this 
converter  may  be  considered  as  a  type,  its  charac- 
teristic being  the  manner  in  which  the  ends  of 
the  core  are  finished.  The  iron  wire  is  permitted 


TRANSFORMERS. 


to  extend  considerably  beyond  the  coils,  the  wires 
being  bent  into  a  radiating  form,  so  that  «ach 
individual  wire  is  separated  from  its  neighbors,  the 
whole  having  the  general  appearance  of  a  brush. 
This  construction  serves  to  equally  disseminate 
the  lines  of  force  through  the  surrounding  space, 
and  results,  according  to  the  inventor,  in  especial 
efficiency.  This  theory  deserves  attention,  and  is 
the  subject  matter  of  an  appendix. 

One  of  the  most  important  points  in  transformer 
construction  is  the  selection  of  the  iron.  Gener- 
ally speaking,  it  is  safe  to  say  that  the  selection  of 
the  iron  is  one  of  the  most  important  preliminaries 
of  transformer  construction.  Not  only  is  the 
purity  of  the  iron  important,  but  also  its  texture, 
fibre  and  malleability.  Iron  of  great  purity  should 
be  selected.  In  other  words,  iron  that  is  as  free 
as  possible  from  carbon,  phosphorus,  silicon,  etc. 
This  may  be  determined  by  chemical  analysis.  A 
high  quality  of  Swedish  soft  sheet  is  probably  as 
good  as  anything  that  can  be  selected,  although 
some  of  the  very  high  grade  English  irons  are 
excellent.  The  metal  should  be  as  soft  and  uni- 
form as  possible,  that  is,  it  should  be  thoroughly 
well  annealed.  The  iron  which  can  be  bent  the 
greatest  number  of  times  without  breaking  may, 
as  a  rule,  be  safely  selected  as  the  best,  provided 
the  analyses  have  proved  it  to  be  pure,  which,  with 
rare  exceptions,  will  be  found  to  be  the  case. 


TKA.N.-J  OJi.MEK    CONSTRUCTION.  83 

Such  an  iron  should  have  rather  high  tensile 
strength,  and  should  show  a  high  per  cent  of  elon- 
gation before  breaking.  Recent  practice  has 
pointed  towards  certain  grades  of  low  steel,  as 
possessing  many  good  qualities  for  transformer 
construction,  but  suitable  steel  is  probably  more 
difficult  to  obtain  than  is  good  iron. 

The  iron  being  selected,  the  next  step  in  the 
manufacture  is  the  punching  of  the  plates  (we  are 
dealing  with  the  now  almost  universal  "block" 
type  of  converter).  This  is  accomplished  upon  a 
power  stamp  or  press,  by  means  of  dies.  The 
sheet  metal  is  placed  upon  the  lower  die,  which  is 
held  stationary,  whilst  the  upper  die  is  brought 
down  upon  it,  punching  out  the  requisite  shape. 
Where  both  an  outer  shape,  and  a  hole,  are  to  be 
cut  out,  it  is  a  common  practice  to  accomplish  the 
operation  by  a  single  blow,  instead  of,  as  formerly, 
using  two  dies  and  presses.  This  is  done  by  using 
what  is  termed  a  "leading  "  die,  one  form  of  which 
is  shown  in  Fig.  23.  There  are  many  modifications 
of  this  plan,  and  it  is  used  in  the  manufacture, 
from  sheet  metal,  of  many  hundreds  of  articles. 
There  is  almost  always  some  automatic  device  for 
freeing  the  metal  after  punching.  A  good  set  of 
dies  should  leave  only  a  very  light  burr  at  the 
edges  of  the  punchings,  whilst  poor  dies  will  leave 
a  heavy  one. 

The  plates  being  punched,  the  next  step  is  the 


84 


TRANSFORMERS. 


building  up  of  the  core.  The  direction  of  the 
lamination  is  already  understood  by  the  reader,  it 
having  been  dealt  with  in  Chapter  II,  when  dis- 
cussing Eddy  currents.  If  the  transformer  core 
is  of  the  class  which  has  abutting  edges  at  the 
break,  then  the  iron  is  built  up  quite  independent 
of  the  coils.  If  of  the  class  which  has  overlapping 
edges,  then  it  is  built  up  within  the  coils.  In 
either  case  the  general  plan  is  the  same. 

As  has  been  stated,  next  each  sheet  of  iron  must 
be  placed  a  layer  of  insulating  material.     Only  a 


very  low  insulation  is  needed,  for  the  potential  of 
Foucault  currents  is  invariably  low.  Practice 
differs  as  to  the  best  and  easiest  method  of  accom- 
plishing this  end.  Some  makers  shellac  or  enamel 
the  plates,  and  then  bake  them  in  an  oven  to  set 
the  coating.  Others  rust,  or  oxidize  the  plates, 
rust  being  an  insulator,  or,  rather,  a  semi-conductor 
of  sufficiently  high  resistance  for  this  purpose. 
Probably,  however,  thin  tissue  paper  is  more  uni- 


TRANSFORMER  CONSTRUCTION.  85 

versally  used  for  this  purpose  than  any  other 
insulating  material.  This  paper  is  sometimes 
glued  or  pasted  to  the  iron,  but  more  commonly 
laid  in  loosely,  being  cut  to  the  required  shape  and 
size,  as  are  the  iron  plates. 

In  building  up  the  plates  are  laid  within  a  rack 
or  former,  which  they  fit,  or  if  there  are  holes  in 
the  plates,  as  there  commonly  are,  for  the  binding 
bolts  which  are  frequently  used  to  hold  the  block 
together,  then  the  plates  are  laid  over  pins,  which 
correspond  to  these  holes,  or  even  over  the  bolts 
themselves.  The  necessary  rack,  or  pins,  being 
provided,  the  plates  are  placed  in  position,  a  layer 
of  paper  or  other  insulation  alternating  with  each 
layer  of  iron. 

When  the  requisite  number  of  plates  have  been 
placed,  the  whole  pile  is  subjected  to  heavy  pres- 
sure, thereby  reducing  it  as  nearly  as  possible  to 
the  nature  of  a  solid  mass.  After  this  operation 
it  is  tightly  bound  together,  either  by  binding 
bolts  passing  through  all  of  the  plates,  or  by 
clamps  on  the  outside.  Where  the  binding  bolts 
are  used  they  should  be  surrounded  by  an  insu- 
lating bushing,  interposed  between  them  and  the 
core,  and  should  have  a  washer  of  insulating 
material  under  both  the  head  and  the  nut. 

The  iron  being  now  ready  for  assembling, 
we  may  turn  our  attention  to  the  winding  and 
insulation  of  the  coils.  This  is  a  comparatively 


TRANSFORMERS. 


simple  matter,  and  is  carried  out  in  the  same 
general  manner,  whether  the  coils  (primary  and 
secondary )  are  made  up  independently,  or  together, 
to  fit  over  one  another,  or  to  be  placed  side  by  side. 

Insulation  is,  generally  speaking,  the  most  vital 
consideration,  but  this  important  question  will  be 
considered  later. 

The  coils  are  wound  in  a  lathe,  upon  a  former 
or  mandril,  having  perpendicular  ends  like  a  spool, 
to  hold  the  wire  on,  and  to  determine  the  width  of 
the  coil.  One  of  these  ends  is  removable,  to 
permit  of  the  coils  being  taken  off  when  completed. 
Double  cotton  covered  wire  is  used,  generally 
spoken  of  as  D.  C.  C.  wire.  One  end  of  the  wire, 
to  be  wound  up,  being  made  fast,  the  "former," 
or  mandril,  is  set  in  motion  in  the  lathe,  the  wire, 
as  it  is  wound  on,  being  drawn  through  tension 
pulleys  to  insure  its  being  wound  on  straight  and 
level.  The  wire  is  watched  and  guided  at  the 
mandril,  to  insure  its  being  wound  on  smoothly 
and  progressively.  When  a  layer  is  completed  it 
is  quite  customary  to  give  the  surface  a  thin  coat  of 
shellac  before  winding  the  wire  back  over  itself. 
In  winding  the  primary  coils  of  large  high  voltage 
converters,  it  is  quite  customary  to  insert  some 
kind  of  insulating  material,  in  addition  to  the 
shellac,  between  each  layer,  to  prevent  the  differ- 
ence of  potential  between  the  layers  from  short- 
circuiting,  inner  and  outer  turns. 


TRANSFORMER   CONSTRUCTION.  87 

When  the  requisite  number  of  turns  have  been 
wound  onto  the  former,  the  wire  is  cut  off  and  the 
coil  removed,  it  having  previously  been  tied  firmly 
together  at  four  or  five  points,  by  pieces  of  twine 
or  tape  placed  on  the  mandril  before  the  winding 
began.  With  the  exception  of  the  care  required 
in  insulating,  primary  coils  are  far  less  difficult  to 
wind  than  secondary,  owing  to  the  fact  that  the 
wire  is  much  finer  and  more  manageable.  As  the 
heavy  wire  necessary  for  the  secondaries  of  large 
capacity,  low  potential  transformers  is  often  most 
unmanageable,  amounting  almost  to  rod,  copper 
tape  is  at  times  substituted  for  this  heavy  wire, 
with  good  results.  The  most  popular  plan,  how- 
ever, is  to  wind  a  number  of  wires  in  multiple,  or 
even  to  place  several  coils  in  multiple. 

Too  much  care  cannot  be  exercised  to  prevent 
any  portion  of  wire,  however  small,  which  is  bared 
of  its  insulation,  from  being  wound  on.  Such  a 
spot,  if  present,  would  almost  certainly  make 
trouble  eventually  by  coming  in  contact  with  other 
bare  metal,  and  causing  a  short  circuit.  When 
such  a  point  is  discovered  in  the  wire  it  should  be 
carefully  wrapped  with  adhesive  rubber  tape  and 
shellaced  before  being  wound  on.  If  the  rubber 
tape  is  too  bulky,  as  it  frequently  will  prove  to  be, 
then  narrow  silk  tape  or  ribbon  may  be  used,  it 
being  made  to  adhere  by  means  of  shellac.  If  it 
becomes  necessary,  for  any  purpose,  to  make  a 


TRANSFORMED. 


joint  in  the  wire  of  an  incompleted  coil,  it  should 
always  be  soldered,  as  well  as  twisted,  and  should 
be  over-wound  with  tape  as  already  described. 
Above  all  things,  great  care  should  always  be  used 
to  see  that  there  are  no  sharp  edges  or  projections 
at  the  joint,  which  might  chafe  through  the  insu- 
lation and  expose  the  metal. 

In  the  case  of  high  potential  transformers  of 
large  capacity,  it  is  a  common  and  excellent  prac- 
tice to  wind  the  primary  in  several  separate  and 
distinct  coils,  which  can  afterwards  be  connected 
in  series,  thus  preventing  any  two  turns  of  wire, 
with  a  considerable  difference  of  potential,  from 
crossing.  If  they  did  so  the  insulation  would 
almost  certainly  chafe  through  and  a  short  circuit 
result 

All  of  the  above-mentioned  contingencies  having 
received  due  and  proper  attention,  the  coil  may  be 
removed  from  the  "former"  without  fear  of  future 
trouble. 

The  next  operation  is  the  taping  of  the  coils. 
An  ordinary  cotton  tape,  from  an  inch  to  an  inch 
and  a  half  in  width,  is  commonly  used  for  this 
purpose.  One  end  of  the  tape  is  made  fast  to  the 
coil  with  melted  shellac,  the  covering  then  being 
wound  on  and  over  the  coil  progressively.  When 
the  coil  is  intended  to  carry,  or  be  brought  into 
close  proximity  to  high  pressure,  it  is  preferable  to 
insert  a  layer  of  insulating  material  below  the 


TRANSFORMER   CONSTRUCTION.  89 

outer  covering  of  tape,  mica  is  probably  the  best 
substance  for  this  purpose.  It  should  be  put  on  over 
a  layer  of  heavy  shellac,  and  should  have  another 
coating  of  thin  shellac  before  the  tape  is  applied. 
Mica  is  very  brittle,  and  great  care  should  be 
exercised  to  prevent  its  breaking  and  chipping  off 
at  corners  and  curves.  Other  substances  are 
frequently  used  instead  of  mica,  such  as  asbestos 
paper,  vulcanized  fiber,  shellaced  paper,  etc.,  but 
whilst  far  more  easy  to  manipulate  than  mica, 
they  are  inferior  to  it,  owing  to  the  fact  that  they 
absorb  moisture  more  or  less  rapidly,  which 
speedily  destroys  their  insulating  qualities  until 
they  are  again  dry. 

No  mention  has  been  made  as  yet  of  what  is 
done  with  ends  of  primary  and  secondary  coils. 
They  are,  of  course,  brought  out  through  the  tape, 
and  this  should  be  done  in  such  a  way,  that  their 
positions  may  be  comparatively  remote  from  one 
another,  since  contact  between  the  two  terminal 
wires,  especially  of  the  primary  coil,  even  though 
well  insulated,  would  be  most  dangerous,  and 
might  at  any  time  result  in  a  short  circuit  and  a 
burn-out.  The  terminal  wires  should  be  carefully 
taped  and  shellaced,  both  for  the  sake  of  the  in- 
sulation, and  the  protection  which  the  covering 
affords  to  the  wire.  It  is  a  common  plan  to  bring 
out  the  ends  of  the  primary  coil  at  one  end  of  the 
transformer,  and  the  secondaries  at  the  other.  A 


90  TRANSFORMERS. 

sufficient  length  of  wire  is  left  to  permit  of  making 
the  necessary  connections  to  the  binding  posts,  or 
terminal  blocks,  which  will  be  presently  mentioned. 

On  completion,  the  coils  are  given  a  final  coat- 
of  shellac,  after  which  they  are  sometimes  baked  in 
an  oven,  to  thoroughly  dry  them  out  and  harden 
the  shellac,  but  this  is  not  always  necessary,  since 
the  completed  transformer  is  generally  baked  as  a 
whole  before  being  enclosed  within  its  case. 

The  finished  coils  are  next  placed  upon  the  iron 
in  their  proper  position,  where  they  should  fit 
closely,  due  insulation  (dependent  upon  the  pres- 
sure for  which  they  are  intended)  being  interposed. 
Mica,  rubber,  vulcanite,  fibre,  asbestos  and  wood, 
are  the  substances  commonly  used  for  insulation 
in  transformers. 

There  is  often  a  space  between  iron  and  wind- 
ings, at  the  bend  at  each  end  of  the  coils,  caused 
by  the  coils  not  making  a  square  turn  and  lying 
flat  upon  the  core.  A  wooden  block,  or  wedge,  is 
frequently  inserted  at  these  two  points,  to  ren- 
der the  whole  solid.  Teak,  or  failing  that,  a 
very  resinous  pine  is  probably  the  best  wood  as 
regards  insulating  qualities,  for  use  in  transformer 
construction.  The  coils  being  in  position  and  the 
two  portions  of  the  core  being  brought  together 
and  firmly  fastened,  either  by  clamping  screws  or 
bolts,  the  transformer  is  complete  and  ready  for 
baking,  to  which  process  it  is  at  once  submitted, 


TRANSFORMER   CONSTRUCTION.  91 

being  placed  in  an  oven  which  is  at  a  temperature 
as  high  as  the  insulation  will  bear  without  injury. 
This  thoroughly  dispels  all  moisture  and  sets  the 
shellac  hard,  so  that  it  resembles  lacquer.  On 
being  removed  from  the  oven,  and  cooled,  the 
transformer  only  lacks  testing,  casing  and  con- 
necting, to  be  ready  for  commercial  use. 

A  thin  cast-iron  box  or  case  is  used  to  enclose 
the  transformer.  Although  this  case  varies  greatly 
in  details  of  construction,  it  is  always  water-proof 
and  usually  has  some  provision  for  ventilation,  a 
ring  bolt  for  lifting,  lugs  and  holes  for  lag  screws, 
by  which  it  may  be  fastened  up.  Terminal  blocks 
are  set  into  it,  but  insulated  very  carefully  from 
it,  and  these  blocks  should  be  so  placed  as  to  pre- 
clude any  possibility  of  a  short  circuit  between 
them.  The  two  ends  of  the  primary  and  secondary 
coils  are  fastened  to  these  blocks  from  the  inside, 
and  the  ends  of  the  leading-in  wires  from  the  main 
circuit  to  the  primary,  and  the  leading-out  wires 
from  the  secondary  to  the  lamps,  are  fastened  into 
these  terminals  by  means  of  set  screws  when  the 
transformer  is  put  into  use.  The  greatest  care 
should  be  exercised  to  prevent  the  necessity  of 
crossing  either  the  primary  or  secondary  inside 
leads  to  get  them  to  their  binding  posts.  This  is 
especially  important  in  connection  with  the  pri- 
mary, as,  if  they  cross,  a  short  circuit  is  very  likely 


TRANSFORMERS. 


to  result,  if  the  insulation  of  the  leads  becomes 
chafed  at  the  point  of  contact. 

It  is  a  common  practice  to  have  an  internal 
arrangement  whereby  fuses,  which  can  readily  be 
replaced,  are  interposed  between  the  terminal  wires 
of  the  coils  and  the  binding  posts,  sometimes  in 
connection  with  the  primary  coil  only  and  some- 
times with  both.  Such  arrangements  are  generally 
mounted  on  porcelain,  and  placed  within  a  sepa- 
rate compartment  of  the  transformer  case,  which 
can  readily  be  opened  to  replace  a  burned  out  fuse. 
Secondary  transformer  fuses,  though  often  found, 
are,  generally  speaking,  uncalled  for.  Although, 
till  recently,  fuses  have  almost  invariably  been 
placed  within  the  transformer,  it  is  probably  better 
to  have  them  outside  instead,  in  an  accessible  po- 
sition, and  this  plan  is  rapidly  finding  favor. 

Many  manufacturers  have  their  transformei 
cases  so  constructed  that  the  fuses  cannot  be 
reached  without  breaking,  or  opening  the  circuit. 
As  a  safety  device  this  is  excellent,  as  many 
accidents  have  occured  from  carelessness  in  put- 
ting in  new  fuses  on  "  live  "  circuits. 

One  of  the  most  radical,  and  marked  improve- 
ments in  modern  transformer  construction,  is  the 
introduction  of  oil  insulation,  the  most  perfect  and 
efficient  insulation  known  for  this  class  of  work. 
Where  this  is  used,  the  entire  transformer  is  sub- 
merged in  a  heavy  low  grade  oil,  specially 


TRANSFORMER  CONSTRUCTION.  93 

prepared  for  the  purpose,  and  closely  resembling 
a  low  grade  of  cylinder  oil.  This  dense  fluid 
speedily  penetrates  every  crevice  of  the  transform- 
er, and  becomes  a  perfect  insulating  film  at  every 
point  of  danger,  precluding  besides  any  possibility 
of  moisture. 

If  a  puncture  or  short  circuit  occurs  at  any 
point,  from  coil  to  coil,  or  from  coils  to  iron,  the 
oil  at  once  penetrates  and  re-insulates  the  crevice, 
rendering  the  point  where  the  discharge  took  place 
as  perfect  as  before,  thus  it  may  be  said  that  trans- 
formers, with  oil  insulation,  are  self -repairing. 

Converter  testing  in  practice,  is  a  comparatively 
simple  matter.  The  points  to  determine,  are  the 
thorough  insulation  of  the  coils  from  one  another, 
and  from  the  iron  and  casing.  The  fitness  of  the 
transformer  to  carry  its  normal  load  indefinitely, 
its  ability  to  bear  its  normal  voltage,  or  a  greater 
pressure,  without  breaking  down  ;  and  the  ratio  of 
conversion,  to  make  sure  that  the  right  number  of 
turns  are  present,  or  that  the  voltage  of  the  second- 
ary is  correct,  with  normal  primary  pressure. 

To  test  the  insulation,  a  magneto  capable  of 
ringing  through  a  high  resistance  is  applied.  The 
contact  points  of  the  magneto  should  be  applied 
first  to  the  end  of  the  primary  and  secondary  coils, 
then  to  primary  and  iron,  and  to  secondary  and 
iron.  If  the  insulation  is  perfect  no  ring  will  be 
obtained.  Some  makers  test  by  attaching  primary 


TRANSFORMERS. 


to  one  side  and  secondary  to  the  other  side  of  a 
very  high  potential  circuit,  of  say  five  or  six 
thousand  volts.  The  insulation  should  stand  this 
without  breaking  down. 

To  test  the  ability  of  the  transformer  to  carry 
normal  load,  and  bear  normal  pressure,  it  is  only 
necessary  to  place  it  on  a  standard  primary  pres- 
sure, load  it  to  its  full  capacity  of  lamps  and  leave 
it  there  for  some  hours,  testing  the  voltage  on 
primary  and  secondary  at  the  end  of  the  run  to 
determine  that  the  ratio  of  conversion  is  correct. 

The  converter  having  stood  these  tests,  is  fin- 
ished and  ready  for  shipment  and  service. 

We  have  endeavored  to  carry  the  reader  with  us 
through  the  path  of  construction  in  its  main  feat- 
ures, from  the  transformer's  component  parts  to 
its  completion,  and  it  now  only  remains  to  us,  to 
add  a  few  points  of  great  importance,  which  should 
be  borne  constantly  in  mind,  to  obtain  the  best 
results. 

1st.  Never  permit  two  wires  with  any  great  dif- 
ference of  potential  to  cross  each  other.  Such 
construction  invites  a  short  circuit. 

2d.  Allow  ample  sectional  area  of  copper,  (800 
to  1000  circular  mills  per  ampere, )  otherwise  the 
converter  will  run  too  warm,  and  give  poor  results. 

3d.  Better  use  too  much  than  too  little 
insulation. 

4th.  Do  not  attempt   to  work  the  iron  at   too 


TRANSFORMER   CONSTRUCTION.  95 

high  a  point  of  saturation,  that  is  at  too  high  an 
induction,  it  is  not  economical. 

5th.  Clamp  the  iron  and  bind  the  coils  rigidly, 
if  this  is  not  done  the  transformer  may  hum. 

6th.  Ventilation  is  an  excellent  thing,  but 
moisture  is  dangerous  and  distinctive. 

7th.  Keep  the  primary  and  secondary  terminals 
well  apart. 

8th.  Do  not  let  any  iron  chips,  or  filings,  get 
into  the  transformer,  they  will  make  their  way 
through  almost  any  insulation  by  magnetic  pro- 
pulsion, and  perhaps  cause  a  short  circuit. 


96  TRANSFORMERS. 


CHAPTER   VI. 

THE   TRANSFORMER    IN    SERVICE. 

IF  the  theory  of  the  transformer  is  in  some  of 
its  details  somewhat  intricate,  its  application  is 
simple  and  easy  to  a  degree.  We  have  in  the 
foregoing  pages  treated  here  and  there  of  various 
matters  which  have  direct  bearing  on  the  subject 
of  this  chapter,  and  we  therefore  shall  here  limit 
the  discussion  to  various  important  points  of  detail, 
rather  than  to  any  general  plans  of  arrangements 
of  circuits,  which  are  undoubtedly  already  well 
understood. 

The  question  of  the  location  of  a  transformer 
is  an  important  one,  and  is  scarcely  amenable  to 
any  general  rules  which  could  be  formulated. 

Local  custom  has  much  to  do  with  the  positions 
selected  for  installing  converters.  In  Europe  it 
is  the  general  practice  to  install  them  within  the 
building  whose  lighting  service  they  are  to  main- 
tain, and  for  this  reason  the  transformers  manu- 
factured in  Europe  are  not,  as  a  rule,  enclosed 
within  waterproof  cases.  With  us,  however,  it  is 
the  custom  to  install  converters  on  the  outside  of 
buildings,  or  in  some  position  in  the  open  air,  and 


TRANSFORMER   IN    SERVICE.  97 

this  is  generally  demanded  by  insurance  require- 
ments. 

There  is  an  opportunity  for  the  exercise  of 
much  judgment  in  selecting  the  capacity  of  the 
transformer  required  to  do  certain  work.  It  should 
always  be  borne  in  mind  that  the  nearer  a  trans- 
former operates  to  full  load  the  greater  its  effi- 
ciency will  be,  but  that  an  overload  is  a  bad  thing, 
endangering  the  transformer  and  causing  poor 
regulation.  If  the  transformer  is  to  operate  on  a 
dwelling  house  circuit,  then  the  number  of  lamps 
upon  its  secondary  will  be  considerably  in  excess 
of  the  actual  capacity  required,  for  there  will 
seldom,  if  ever,  be  an  occasion  when  all  of  the 
lamps  will  be  in  service  at  the  same  time.  In  a 
case  of  this  kind  a  close  estimate  of  the  number  of 
lamps  likely  to  be  in  use  at  one  time  will  represent 
the  capacity  required.  If  a  store,  hall,  or  factory 
is  to  be  lighted  it  is  probable  that  all  of  the  lights 
will  be  in  use  at  the  same  time  and,  therefore,  the 
total  number  of  lights  installed  will  represent  the 
size  of  converter  required. 

Large  transformers  are  more  efficient  than  small 
ones,  therefore  they  should  always  be  used  when 
possible.  It  frequently  happens  that  a  number  of 
stores  or  dwelling  houses  requiring  light  are  near 
together.  In  a  case  of  this  kind  one  transformer 
can  be  made  to  do  the  work  for  the  Avhole  number, 
it  being  installed  as  nearly  as  possible  at  the  centre 


98  TRANSFORMERS. 

of  consumption,  and  its  secondary  being  divided 
and  carried  to  the  various  installations,  as  sepa- 
rate secondary  circuits.  This  practice,  if  generally 
followed,  will  result  in  economy,  though,  of  course, 
the  secondary  must  not  be  carried  through  any 
considerable  distance,  or  the  C2R  loss  will  become 
excessive  and  wasteful. 

There  is  an  opportunity  also  for  the  exercise  of 
much  judgment  in  determining  the  best  secondary 
potential  to  be  used.  If  the  total  secondary  circuit 
is  short,  then  50  to  52  volts  is  the  best  pressure  to 
use,  for,  though  the  amount  of  copper  required 
will  be  considerable,  lamps  of  this  potential  are 
somewhat  more  efficient.  If  the  length  of  second- 
ary wiring  be  considerable,  then  it  is  generally 
preferable  to  use  a  pressure  of  100  to  104  volts, 
because  of  the  resultant  saving  in  wire,  and  the 
reduction  of  C2R  loss.  Where  a  large  building  is 
to  be  wired  and  the  total  length  of  secondary 
wiring  is  great,  it  is  a  frequent  and  excellent  prac- 
tice to  bank  two  transformers  and  do  the  wiring 
on  the  three-wire  plan.  Directions  for  doing  this 
will  be  found  later  in  this  chapter. 

Where  the  number  of  lights  to  be  carried  on  one 
circuit  is  greater  than  the  capacity  of  a  single 
converter,  a  number  may  be  arranged  in  multiple, 
as  shown  in  Fig.  24.  When  this  is  done  however, 
the  transformers  used,  should  always  be  of  the 
same  capacity,  and  the  same  style.  It  must  be 


TKANSFOKMER  IN   SERVICE. 


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100  TRANSFORMERS. 

borne  in  mind,  that  if  the  primary  fuse  of  one  of 
several  banked  transformers  "blows"  then  the 
secondary  of  that  transformer  becomes  a  load 
upon  the  rest  of  the  bank,  in  addition  to  the  por- 
tion of  the  load  it  was  carrying.  Under  this 
extra  strain,  the  fuses  of  the  remaining  trans- 
formers, will  probably  blow  also,  and  darkness  and 
confusion  result. 

For  this  reason  it  is  generally  preferable  to 
divide  all  circuits  when  possible,  using  single 
transformers,  so  that  all  of  the  lamps  in  a  building, 
may  not  be  dependent  on  a  single  source.  When 
banking  is  unavoidable,  it  is  an  excellent  plan  to 
insert  a  large  main  circuit  fuse  on  the  united 
secondary  of  the  whole  bank,  calculated  to  blow 
before  the  individual  transformer  fuses,  thus,  if  all 
of  the  lamps  go  out,  they  can  be  re-lighted  by 
the  insertion  of  a  single  fuse  instead  of  one  in 
each  transformer.  It  is  of  course  understood  that 
there  are  always  a  number  of  sub-circuit  fuses 
between  the  lamps  and  the  bank. 

At  times  it  becomes  necessary  to  so  bank  trans- 
formers, as  to  get  an  increased  potential.  For  ex- 
ample, a  building  may  be  ready  wired  on  a  basis 
of  100  volts,  the  lamps  being  made  for  100  volts 
also,  whilst  the  only  transformers  available  are 
designed  to  give  a  secondary  potential  of  50  volts. 
In  this  case  the  transformer  must  be  banked  with 
two  secondaries  in  series,  as  shown  in  Fig.  25. 


TRANSFORMER   IN   SERVICE.  101 

It  is  well  to  remember  that  when  two  or  more 
transformers  are  connected  with  their  secondaries  in 
multiple,  their  united  output  is  equal  to  the  sum  of 
their  rated  current  at  their  normal  potential. 

When  banked  with  their  secondaries  in  series, 
their  output  is  equal  to  the  sum  of  their  rated  po- 
tentials, with  current  equal  to  the  rating  of  one 
transformer.  (All  of  the  converters,  of  course, 
being  of  the  same  capacity.) 

To  bank  transformers  to  operate  on  the  three- 
wire  plan  they  should  be  arranged  with  their  pri- 
maries in  multiple,  as  is  usual,  and  their  secondaries 
in  series,  with  the  neutral,  middle,  or  third  wire 
taken  off  between  them,  as  shown  in  Fig.  26. 

This  is  generally  done  with  100  volt  transform- 
ers, and  saves  much  wire,  the  greater  portion  of 
the  energy  being  distributed  at  200  volts,  and  the 
lamps  (which  are  100  volts)  burning  two  in  series, 
except  when  more  are  in  use  on  one  side  than  on 
the  other,  in  which  case  the  middle  wire  takes  care 
of  the  difference.  The  two  outside  wires  are  to  be 
figured  upon  on  the  basis  of  200  volts,  and  the 
middle  wire  should  have  from  one-half  to  one-third 
of  the  carrying  capacity  of  the  outside  wires.  The 
lamps  must,  of  course,  be  distributed  about  equally 
between  the  two  sides.  The  main  fuse  on  the 
middle  wire  must  have  a  capacity  in  excess  of  its 
calculated  load,  for  if  it  burns  out  many  of  the 
lamps  on  one  side  will,  as  a  rule,  be  destroyed  by 


102  TKANSFOEMERS. 


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TRANSFORMER   IK    SERVICE.  103 

the  passage  of  excessive  current,  due  to  the  un- 
balanced condition  of  their  resistance.  The  main 
fuse  on  the  middle  wire  is  frequently  altogether 
omitted. 

Transformers  are  frequently  incorrectly  ar- 
ranged on  the  three-wire  plan.  A  common  but 
very  incorrect  method  is  shown  in  Fig.  27.  The 
error  here  is  in  the  primary  connections,  opposite, 
instead  of  similar  wires  (as  when  correct),  being 
connected  to  the  same  side  of  the  primary.  There 
is  no  saving  of  wire  in  this  plan,  over  the  ordinary 
two-wire  arrangement.  It  has  no  advantages,  and 
should  be  avoided. 

Some  commercial  transformers  are  so  con- 
structed that  by  changing  simple  internal  connec- 
tions, they  will  give  either  52  or  104  volts  at  the 
secondary  as  required,  the  output  representing  the 
same  amount  of  power  in  either  case.  This  plan 
is  an  excellent  one  and  of  great  convenience. 

Transformers  should  be  placed,  when  out  of 
doors,  either  011  the  side  of  a  building,  or,  still 
better,  upon  a  pole  when  available,  the  latter  posi- 
tion being  preferable  on  account  of  the  vibration. 
Jar,  within  certain  limits,  is  an  excellent  thing  for 
transformers,  and  should  be  sought  rather  than 
avoided,  since,  as  we  have  seen  in  Chapter  II,  it 
tends  to  reduca  the  hysteresis  loss,  and  to  render 
the  converter  more  efficient. 

Many  transformers  are  provided  with  hooks,  or 


104  TRANSFORMERS. 

a  kind  of  elbow  at  their  upper  end,  by  means  of 
which  they  can  be  suspended  from  the  arm  of  a 
pole,  or  from  a  cleat  attached  to  a  wall.  This  is  a 
great  convenience  and  saves  much  labor.  Gener- 
ally speaking,  however,  they  are  fastened  up  by 
means  of  lag  screws. 

If  it  can  be  avoided,  transformers  should  never 
be  placed  against  metal,  such  as  a  tin  roof  or  metal 
shingled  wall,  as  there  is  always  danger,  in  a  case 
of  this  kind,  of  a  "'  ground  "  on  one  side  of  the  line 
and  consequent  trouble.  It  is  also  a  bad  practice 
to  lay  converters  on  their  sides  or  backs,  in  posi- 
tions where  they  are  liable  to  be  exposed  to  wet. 
This  is  frequently  done,  but  is  none  the  less  to  be 
avoided.  The  upper  end  of  the  case  is  designed  to 
withstand  rain,  while  the  remaining  portions  of 
the  box  are  not  always  absolutely  waterproof  in 
case  of  a  heavy  downpour,  and  if  water  penetrates 
within,  trouble  is  more  than  likely  to  result. 

In  some  localities,  where  violent  electrical 
storms  are  prevalent,  notably  the  Southern  coun- 
tries, considerable  damage  is  at  times  caused  to 
transformers  by  lightning.  In  such  cases  it  is  not 
necessary  that  a  lightning  discharge  should  "strike" 
the  converter  or  its  wires,  though  this  at  times 
occurs.  Often  the  trouble  results  from  a  secondary 
current,  induced  by  the  lightning,  generally  in  the 
main  primary  circuit.  The  effect  which  this  has  upon 
the  converter  varies  greatly  with  the  conditions. 


TRANSFORMER   IN   SERVICE.  105 

At  times  it  simply  blows  the  primary  fuses,  at 
others  it  melts  a  portion  of  the  primary  coil.* 
More  commonly,  however,  it  punctures  the  insula- 
tion, striking  through  either  to  the  secondary  coil, 
the  hon,  or  both,  at  times  leaving  no  evidence  of 
the  mischief  which  has  been  wrought;  it  is  this 
last  contingency  that  is  most  to  be  dreaded,  for  it 
may  contain  an  element  of  clanger. 

The  primary  having  a  path  to  the  secondary  on 
one  side  may,  if  a  "  ground  "  occurs  upon  the  other, 
send  a  dangerous  shock  through  the  secondary,  pro- 
vided anyone  should  come  in  contact  with  a  portion 
of  the  secondary  circuit  in  such  a  manner  as  to  con- 
nect it  to  the  ground  through  themselves.  Such  a 
combination  of  circumstances  is  of  necessity  rare, 
however,  and  there  is  probably  only  one  authentic 
case  of  disaster  on  record,  resulting  from  this  state 
of  affairs. 

It  is  in  connection  with  punctures,  due  to 
lightning,  etc.,  that  the  system  of  oil  insulation 
is  of  greatest  value,  for  every  puncture  is  re-insu- 
lated by  the  oil  as  soon  as  made,  leaving  the  trans- 
former practically  as  perfect  as  before,  Another 
safety  device,  which  has  been  adopted  in  some 
transformers,  in  connection  with  lightning  dis- 
charges, calculated  to  prevent  injury  to  the  coils, 
is  the  grounding  of  the  iron  core.  This  is  accom- 

*  This  latter  result  is  rare,  but  has  been  observed.    When  the  fuses 
blow,  they  must  have  drawn  an  arc,  which  maintained  the  circuit. 


106  TRANSFORMERS. 

plished  by  connecting  the  laminated  plates  either 
to  water  or  damp  earth  by  means  of  a  copper  wire. 
Since  lightning  invariably  seeks  the  shortest  path 
to  the  earth,*  it  will,  when  the  core  is  grounded, 
strike  through  the  insulation  to  the  lamination, 
and  thence  go  directly  to  earth,  when  if  oil  insu- 
lation be  present  it  will  immediately  re-insulate 
the  puncture,  leaving  the  transformer  in  perfect 
working  condition.  When  the  core  is  grounded 
in  this  way  it  must,  of  course,  be  strictly  insulated 
from  the  case.  It  is  naturally  understood  that  the 
potential  of  a  lightning  discharge  is  practically 
irresistable. 

The  primary  fuses  in  the  transformer,  and  in 
fact  everywhere,  should  have  a  rubber  covering 
over  the  lead  and  tin  wire  of  which  they  are  made. 
Primary  fuses  are  now  constructed  in  this  way. 
The  rubber  covering  prevents  the  flash  of  a  burn- 
ing fuse  from  reaching  beyond  its  proper  limits, 
and  also  tends  to  prevent  the  burning  fuse  from 
establishing  an  arc  between  its  terminals. 

When  not  enclosed  within  the  transformer,  pri- 
mary fuses  should  be  placed  out  of  doors,  within 
boxes  manufactured  for  their  reception,  and  in  a 
readily  accessible  position,  conveniently  near  the 
transformer.  Both  the  main  and  sub-circuit  sec- 
ondary fuses  should  be  placed  indoors,  in  a  position 
where  they  can  be  readily  reached. 

*  The  shortest  electrical  path,  i.  e.,  the  path  of  least  resistance. 


TRANSFORMER  IN  SERVICE.  107 

In  very  long  distance  distribution  it  has  some- 
times been  found  advantageous  to  introduce  step- 
up  transformers,  to  raise  the  output  of  the  dynamo 
to  a  yet  higher  pressure  (5,000,  and  even  10,000 
volts),  at  which  potential  it  is  carried  very  great 
distances  with  remarkably  little  loss,  and  on  rela- 
tively smaller  wire,  to  the  distributing  point,  where 
it  is  again  reduced  to  customary  distributing  pres- 
sure, and  carried  over  ordinary  circuits  to  the 
house  transformers,  the  energy  thus  being  trans- 
formed three  times  before  reaching  the  lamps. 
This  system  is  valuable  in  that  it  renders  possible 
the  utilization  of  large  water-powers,  remote  from 
points  of  usefulness.  The  plan  is  quite  popular  in 
Europe,  but  much  less  so  in  this  country.  Of 
course  the  great  difficulty  to  be  met  lies  in  pro- 
viding the  insulation  requisite  for  such  high 
voltages.  Further  information  relative  to  this 
subject  will  be  found  in  an  appendix. 

It  will  sometimes  be  noticed  that  transformers 
emit  a  humming  noise,  which  is  occasionally  so 
loud  as  to  be  annoying.  This  will  be  especially 
noticeable  if  the  converters  are  carrying  an  over- 
load. The  noise  is  caused  by  the  rapid  vibration 
of  the  iron  plates  of  the  lamination  ;  and  sometimes 
even  by  the  coils  themselves,  resulting  from  the 
rapid  attraction  and  repulsion  of  the  iron  plates  of 
the  lamination,  and  also  of  the  individual  turns  of 
the  coils.  The  more  tightly  the  plates  are  clamped 


108  TRANSFORMERS. 

together,  and  the  more  closely  the  coils  are  bound, 
the  less  the  transformer  will  hum,  in  fact,  well 
constructed  transformers  seldom  hum  noticeably, 
even  upon  considerable  overloads. 

There  are  several  very  important  points  in  con- 
nection with  the  installation  of  transformers  which 
should  be  carefully  borne  in  mind.  An  endeavor 
is  here  made  to  condense  these  into  a  few  terse 
and  clear  sentences. 

1.  Remember  that  the  larger  wires  are  the  sec- 
ondary connections  and  go  to  the  lamps. 

2.  Do  not  put  in  the  fuses  till  the  transformer 
is  fixed  in  position. 

3.  Rubber  covered  fuses  should  be  used  on  the  pri- 
mary circuit. 

4.  Do    not   handle  live  primary  wires  without 
rubber  gloves.     It  is  dangerous. 

5.  Try  to  use  only  one  hand  when  working  about 
live  primary  wires.     It  insures  safety. 

6.  Locate  all  fuses  where  they  can    be   readily 
reached. 

7.  Place  the  main  primary  fuse  out  of  doors  if 
possible,  when  not  enclosed  within  the  transformer. 

8.  Abide  by  the  Underwriters'1  Rules.    (See  Ap- 
pendix.) 

9.  Avoid  making  all  lights  in  a  large  building 
dependent    on   a   single    bank    of    transformers. 
Divide  your  circuits. 


TRANSFORMER   IN    SERVICE. 


10.  In    banking   use   transformers  of  the  same 
type  and  capacity. 

11.  When  banking  connect  similar  leads  of  the 
transformer  to  the  same  side  of  the  primary  line. 

12.  A  slight  amount  of  jar  renders  transformers 
more  efficient. 

13.  Large  transformers  are  more  efficient  than 
small  ones. 

14.  Do  not  use  larger  transformers  than  neces- 
sary.     Transformers  are  most  efficient  on  full  load. 


110  TRANSFORMERS. 


CHAPTER    VII. 

COMMERCIAL  TRANSFORMERS. — FERRANTJ.  — NA- 
TIONAL. —  SLATTERY.  —  STANLEY.  —  THOMSON- 
HOUSTON.—  WESTINGHOUSE. 

IT  has  been  thought  best  to  devote  a  brief  con- 
cluding chapter  to  a  few  of  the  commercial  trans- 
formers which  are  to  be  found  upon  the  market  at 
the  present  time.  The  transformers  mentioned  in 
the  following  pages  do  not  represent  all  that  are 
for  sale  at  the  present  day  by  any  means.  They 
have  been  selected  either  because  of  their  promi- 
nence and  popularity,  or  because  novel  and  typical. 
They  are  all,  with  one  exception,  of  American 
manufacture. 

The  Ferranti  Transformer  is  the  only  converter 
of  foreign  manufacture  of  which  mention  is  to  be 
made  in  this  chapter.  It  has  been  selected  as 
typical,  and  a  good  example  of  European  practice. 

It  will  be  noticed  by  glancing  at  the  accompany- 
ing illustration,  Fig.  28,  that  this  transformer  is  not 
enclosed  within  a  water-proof  case,  as  is  customary 
with  converters  of  American  manufacture.  Such 
a  case  is  not  needed  where  transformers  are  to  be 


COMMERCIAL    TRANSFORMERS. 


Ill 


112  TRANSFORMERS. 

installed  within  buildings,  as  is  usual  in  Europe. 
This  transformer  is  typical,  being  built  on  the  plan 
of  type  4,  Fig.  19,  Chapter  V.  The  frame  which 
holds  and  supports  the  actual  converter  is  of  cast- 
iron,  and  is  so  constructed  as  to  provide  for  stand- 
ing the  transformer  upon  the  floor,  a  basement  or 
dry  cellar  generally  being  the  location  selected. 

The  primary  and  secondary  terminals  are  at 
opposite  ends  of  the  base,  and  are  so  constructed 
that  they  cannot  be  tampered  with,  or  the  wires 
loosened  with  an  ordinary  screwdriver.  The 
terminals  are  thoroughly  insulated  from  the  frame 
by  means  of  sulphur  and  glass  insulation,  poured, 
while  in  a  molten  state,  into  the  space  between  the 
frame  and  each  terminal  block.  No  fuses  are  con- 
tained within  the  converter,  as  it  is  intended  that 
they  should  be  installed  separately. 

The  iron  used  in  the  construction  of  these  trans- 
formers is  extra  soft  Swedish  sheet,  and  is 
unusually  thin.  As  it  is  not  clamped  together, 
however,  the  iron  is  quite  apt  to  be  loose,  and  the 
transformers  have  a  tendency  to  hum.  The  gen- 
eral plan  of  construction  follows  closely  that 
described  under  the  head  of  No.  4,  Chapter  V,  in 
fact,  this  is  probably  the  only  commercial  trans- 
former of  that  type.  Ferranti  transformers  have 
been  constructed  for  service  on  very  high  poten- 
tials, 2400  volts  being  the  commonest  primary 
pressure,  while  large  central  distributing  trans- 


COMMERCIAL    TRANSFORM  Ki:-. 


113 


FIG.  29. 


114 


TRANSFORMERS. 


FIG.  30. 


COMMERCIAL   TRANSFORMERS.  116 

formers  have  been  constructed  for,  and  successfully 
operated  upon,  10,000  volts.* 

This  is  the  class  of  transformer  used  in  connec- 
tion with  distribution  from  the  celebrated  Deptford 
Station,  near  London.  The  chief  merits  claimed 
for  the  Ferranti  converter  are  high  insulation  and 
the  ease  with  which  they  can  be  repaired. 

The  National  Transformer  is  manufactured  by 
the  National  Electric  Manufacturing  Co.,  of  Eau 
Glairs,  Wisconsin.  Its  general  appearance  is 
clearly  shown  by  Fig.  29.  The  transformer  is  of 
the  ring  type,  described  in  Chapter  V  as  No.  2. 
The  entire  winding  is  surrounded  by  iron,  all  of 
the  wire  in  the  transformer  thus  being  active,  and 
high  efficiency  is  claimed  as  the  result.  The  true 
character  of  the  converter  may  be  better  under- 
stood by  referring  to  Fig.  30. 

A  novel  feature  is  the  fuse  and  connection  box, 
which  is  on  the  lower  side  of  the  case.  The  open- 
ing of  the  fuse  box  door  simultaneously  breaks  the 
connection  between  the  primary  wires  and  the  fuse 
contacts,  thus  rendering  it  possible  for  the  primary 
fuses  to  be  quickly  replaced  without  danger  of 
shocks  or  short  circuits,  the  transformer  and  its 
secondary  circuits  being  inactive  when  the  fuse 
box  is  open.  This  safety  device  is  clearly  shown 
by  Fig.  31.  The  case  is  so  constructed  as  to  be 

*  See  Appendix.  * 


116 


TBANSFOKMKKS. 


FlG.    31. 


COMMERCIAL   TRANSFORMERS. 


117 


FIG.  32. 


118  TRANSFORMERS. 

waterproof,  and  ample  provision  is  made  for  ven- 
tilation. 

These  converters  are  manufactured  in  sizes 
ranging  in  capacity  from  two  to  one  hundred 
16-candle  power  lights.  The  safety  device  is  not 
furnished  for  transformers  of  less  than  five,  or 
more  than  fifty  light  capacity.  The  merits  claimed 
are  high  efficiency,  safety,  convenience,  and  close 
regulation. 

The  Slattery  Transformer.  This  converter  is 
manufactured  by  the  Fort  Wayne  Electric  Co.,  of 
Fort  Wayne,  Indiana.  It  is  a  block-shaped  trans- 
former, belonging  to  the  class  described  as  No. 
1,  Chapter  V.  Its  general  character  is  clearly 
shown  by  the  accompanying  cut,  Fig.  32. 

Both  the  primary  and  secondary  leads  enter  at 
the  lower  end  of  the  case,  being  kept  well  apart, 
however.  The  case  is  cast  in  two  nearly  equal 
pieces,  and  is  bolted  together,  as  shown  in  the 
illustration.  Careful  provision  is  made  for  proper 
ventilation,  thus  insuring  cool  running. 

The  ratio  of  transformation  adopted  is  either  20 
or  10  to  1,  50  or  100  volts  being  the  popular  sec- 
ondary potentials.  Efficiency,  simplicity,  safety 
and  careful  construction  are  the  merits  claimed  for 
this  transformer.  It  is  widely  used  and  generally 
gives  excellent  results. 

The  Stanley  Transformer  is  manufactured  by  the 
Stanley  Electric  Manufacturing  Co.,  of  Pittsfield, 


COMMERCIAL   TRANSFORMERS. 


119 


120  TRANSFORMERS. 

Mass.  This  company  devotes  itself  almost  exclu- 
sively to  the  manufacture  of  electrical  converters. 
The  construction  of  the  Stanley  transformer  is 
clearly  shown  in  the  accompanying  illustration, 
Fig.  33.  It  is  here  shown  with  the  fuse  and  con- 
nection box  open,  showing  the  construction.  No 
secondary  fuses  are  used.  The  primary  fuses  are 
mounted  on  movable  porcelain  blocks,  one  of  which 
is  shown  removed  from  its  position. 

In  inserting  new  fuses  it  is  only  necessary  to 
withdraw  the  blocks  from  their  connections,  which 
breaks  the  circuit,  after  which  a  new  fuse  can  be 
set  on  the  block  without  difficulty  or  danger.  It 
is  customary  for  a  station  to  have  a  number  of 
extra  plugs,  that  there  may  be  no  delay  in  insert- 
ing a  new  fuse.  The  same  size  of  plug  fits  all 
different  sizes  of  transformers  up  to  100  lights. 
The  front  plate  of  the  fuse  box  is  held  in  place  by 
two  screws,  and  the  lower  flap  is  held  up  by  a 
thumb-screw,  in  contact  with  a  lip  cast  onto  the 
front  plate.  The  two  fuses  are  entirely  separated 
by  a  porcelain  partition  in  the  fuse  box,  thus  pre- 
venting any  possibility  of  a  short  circuit  from  one 
to  the  other.  The  secondary  connections  are  made 
at  the  lower  end  of  the  transformer. 

In  replacing  fuses  the  front  plate  is  not  removed, 
but  the  lowei-  flap,  or  door,  is  opened  by  loosening 
the  thumb-screw.  The  transformer  is  provided  at 
the  back  with  a  hook  or  elbow,  forming  part  of 


COMMERCIAL,  TRANSFORMERS.  121 

the  case,  thus  rendering  it  easily  placed  in  position. 
It  is  only  necessary  to  hoist  the  transformer  up  by 
the  eyebolt  and  hook  it  over  the  cross-arm,  of  the 
pole,  or  a  timber  on  the  side  of  a  building.  The 
merits  claimed  for  this  transformer  are  high  effi- 
ciency, close  regulation,  small  leakage,  convenience 
and  safety. 

The  Thomson-Houston  Transformer.  This  con- 
verter is  manufactured  by  the  General  Electric 
Co.,  at  their  factory  in  Lynn,  Mass.  It  is  of  the 
block  form,  but  embraces  many  novel  features.  A 
clear  idea  of  the  general  character  of  this  converter 
may  be  obtained  by  glancing  at  Fig.  34.  The 
leading-in  wires  for  both  primary  and  secondary 
are  at  the  top  of  the  case,  which  is  extremely  con- 
venient in  making  connections  with  circuits. 

No  fuses  are  placed  in  the  converter.  The  pri- 
mary fuses  are  placed  within  a  primary  switch  and 
fuse  box,  which  is  always  furnished  with  all 
transformers,  and  is  to  be  placed  in  any  convenient 
position  where  the  fuses  can  be  readily  renewed. 
The  secondary  fuses  are  to  be  placed  within  the 
building  to  be  lighted,  or  near  the  point  where  the 
secondary  wires  enter.  The  fuses  being  thus  dis- 
posed, it  follows  that  the  transformer  case  need 
never  be  opened  after  the  converter  is  installed. 

This  transformer  is  provided  with  the  oil  insu- 
lation already  referred  to  in  previous  chapters. 
Glancing  again  at  the  illustration,  Fig.  34,  it  will 


TRANSFORMERS. 


FIG.   34. 


COMMERCIAL  TRANSFORMERS.  123 

at  once  be  noted  that  the  case  is  constructed  in 
the  form  of  a  kind  of  cup  or  pocket,  the  only 
entrance  being  by  means  of  a  lid,  or  cap  piece,  at 
the  top  of  the  case.  Within  this  complete  recep- 
tacle the  transformer  is  fixed,  and  when  the  appa- 
ratus is  installed  the  case  is  filled  with  oil  supplied 
for  the  purpose,  thus  completely  surrounding  and 
permeating  the  transformer  with  a  very  perfect 
self-renewing  insulating  medium.  It  is  unnecessary 
to  discuss  the  merits  and  advantages  of  oil  insu- 
lation here,  as  they  are  fully  considered  in  a 
previous  chapter.  The  amount  of  oil  required 
with  each  transformer  varies  from  two  quarts  for 
a  600  watt  converter,  to  nine  quarts  in  the  7500 
watt  size. 

Another  safeguard  against  loss  of  insulation  is 
added  by  the  grounding  of  the  core.  The  lami- 
nated iron  is  fully  insulated  from  the  case,  and  is 
connected  thoroughly  to  earth  by  means  of  a 
ground  wire.  Thus  a  lightning  discharge,  entering 
the  converter,  would  strike  through  the  insulation 
from  coil  to  lamination,  and  pass  down  the  ground 
wire  to  earth,  the  puncture  being  immediately 
re-insulated  by  the  oil.  This  matter  was  thorough- 
ly discussed  in  Chapter  VI. 

These  transformers  are  wound  to  stand  a  test  of 
5000  volts  without  oil  insulation. 

The  case  of  the  Thomson-Houston  transformer 
is  provided  with  hooks  to  permit  of  its  being 


124 


TRANSFORMERS. 


FIG.  35. 


COMMERCIAL   TRANSFORMERS.  125 

readily  installed  upon  cross-arms  or  transformer 
timbers  on  houses. 

The  merits  claimed  for  this  converter  are  high 
efficiency,  perfect  insulation,  safety,  long  life,  close 
regulation,  small  leakage,  convenience  and  sim- 
plicity. 

Previous  to  the  introduction  of  the  transformer 
just  described,  which  is  known  as  Type  F,  the 
Thomson-Houston  Electric  Co.  manufactured  a 
transformer  known  as  their  Type  E,  an  illustration 
of  which  is  shown  in  Fig.  35.  This  transformer  is 
widely  used  and  generally  popular. 

The  Westinghouse  Converter  is  shown  in  accom- 
panying illustration,  Fig.  36,  and  is  manufactured 
by  the  Westinghouse  Electric  Co.,  of  Pittsburg, 
Penn.  Like  most  of  the  other  commercial  trans- 
formers it  is  block-shaped. 

At  the  upper  end  of  the  case,  and  attached  to 
the  front  plate,  is  a  fuse  and  connection  box.  This 
contains  a  removable  porcelain  block,  carrying  the 
primary  fuses.  The  removal  of  this  block  breaks 
the  primary  circuit,  leaving  the  converter  dead 
while  the  fuses  are  being  renewed.  New  fuses 
may  thus  be  placed  with  perfect  safety  and  with- 
out trouble. 

The  fuse  box  is  opened  by  removing  the  front 
plate,  which  is  held  in  place  by  three  thumb-screws, 
as  shown  by  the  illustration.  The  front  plate 
cannot  be  dropped,  being  fastened  to  the  converter 


126 


TBANSFOKMERS. 


by  a  chain.  The  secondary  connections  are  made 
at  the  lower  end  of  the  case,  being  remote  and 
thoroughly  isolated  from  the  primary  circuit. 

These  transformers  are   manufactured  in  sizes 
ranging  from  250  to  6250  watts,  and  to  give  sec- 


FIG. 


ondary  potentials  of  50  or  100  volts,  as  is  required. 
The  manufacturers  claim  for  them  high  efficiency, 
good  regulation,  high  insulation,  safety  and  care- 
ful construction. 

In  describing  the  foregoing  transformers  we 
have  endeavored  to  confine  ourselves  strictly  to 
their  more  striking  and  conspicuous  features.  A 


COMMERCIAL   TRANSFORMERS.  127 

general  description  has,  in  every  case,  been  ren- 
dered unnecessary  by  the  excellent  cuts  which  we 
have  been  enabled,  through  the  kindness  of  the 
various  manufacturers,  to  present. 

Although  this  may  justly  be  considered  as  the 
concluding  chapter  of  this  little  work,  there  are 
yet  to  follow  a  number  of  pages  devoted  to  sun- 
dry miscellaneous,  but  distinctly  relevant,  matters 
which,  while  too  important  to  omit,  could  scarcely 
be  classified  under  any  of  the  previous  headings. 


TRANSFORMERS. 


APPENDICES. 

1.  —  HIGH  VOLTAGES.  2.  —  THE  "HEDGEHOG" 
TRANSFORMER.  3. — THE  WELDING  MACHINE. 
4. — DIRECT  CURRENT  TRANSFORMERS.  5. — STA- 
TION TRANSFORMERS.  6. — CONSTANT  CURRENT 
TRANSFORMERS.  7. — UNDERWRITERS'  RULES. 

1.      HIGH  VOLTAGES. 

REFERENCE  has  already  been  made  to  the  use 
of  very  high  pressures  obtained  by  means  of  step- 
up  transformers,  for  distributing  large  amounts  of 
power  through  very  long  distances  with  relatively 
small  loss. 

The  economy  that  would  result  from  such  a 
system  has  long  been  understood,  but  the  many 
serious  difficulties  which  have  stood  in  the  way  of 
its  successful  application  have,  until  recently,  with 
isolated  exceptions,  caused  its  use  to  be  confined 
almost  entirely  to  experiment.  Among  the  earliest 
experiments  with  high  voltages  from  step-up  trans- 
formers (as  distinct  from  static  pressures),  were 
those  conducted  in  London,  just  previous  to  the 
building  of  the  celebrated  Deptford  station.  Their 
purpose  was  to  establish  the  feasibility  of,  and  the 


APPENDICES.  129 

necessary  methods  to  be  pursued  in  a  system  such 
as  that  which  subsequently  resulted. 

In  the  frontispiece  of  this  volume  a  photograph 
is  re-produced,  showing  a  discharge  from  the 
10,000  volt  circuit  of  a  step-up  transformer. 

This  experiment  was  to  establish  the  distance 
that  this  pressure  would  force  current  through  an 
ordinarily  dry  atmosphere. 

The  discharge  depicted  was  between  two  copper 
points,  separated  from  one  another  by  five-eighths 
of  an  inch.  Across  this  open  space  the  enormous 
pressure  caused  the  electric  fluid  to  leap  without 
difficulty. 

Dry  air  being  practically  the  best  insulating 
medium  known,  the  difficulty  of  properly  insulat- 
ing such  high  potentials  will  readily  be  appreciated. 
The  flash  at  the  light  of  the  illustration  is  occa- 
sioned by  the  blowing  of  a  fuse  immediately  upon 
the  establishment  of  the  circuit  through  the  air. 
There  were,  at  the  time  these  experiments  were 
first  attempted,  no  thoroughly  effective  measuring 
instruments  for  computing  what  voltages  really 
existed  at  such  very  high  pressures. 

The  earliest  method  of  definitely  determining 
that  10,000  volts  had  actually  been  obtained  was 
by  illuminating  100  100-volt  lamps  in  series.  This 
required,  of  course,  10,000  volts  between  the  two 
ends  of  the  line  of  lamps,  to  bring  them  to  full 


130 


TKAXSFOKMEI5S. 


APPENDICES.  131 

candle-power.  Such  an  arrangement  is  shown  in 
the  accompanying  illustration,  Fig.  37. 

Many  recent  experiments,  conducted  to  ascer- 
tain the  effects  and  results  which  could  be  obtained 
with  very  high  potentials,  combined,  as  a  rule,  with 
high  frequency  of  alternations,  have  brought  to 
our  knowledge  a  large  number  of  very  beautiful 
and  remarkable  results. 

Thus,  with  a  very  large  induction  coil  or  step-up 
transformer,  having  an  enormous  number  of  turns 
of  very  fine  wire  in  the  secondary,  and  a  very  rapid 
rate  of  alternation  being  used,  the  two  ends  of  the 
secondary,  though  remote  from  one  another,  emit 
a  more  or  less  brilliant  scintillating  light,  surround- 
ing the  ends  of  the  wire.  This  resembles  in 
general  character  and  appearance  that  remarkable 
natural  phenomenon,  which  at  times  appears  at 
the  ends  of  ships'  masts  and  spars,  known  as  St. 
Elmo's  fire. 

Incandescent  lamps,  having  only  a  single  thread 
of  filament,  become  brightly  illuminated  on  being 
attached  to  one  of  the  wires,  while  on  sufficiently 
intensifying  these  conditions  a  simple  incandescent 
lamp  of  peculiar  construction  may  be  illuminated 
without  being  brought  in  contact  with  any  wire 
or  source  of  current  whatever,  and  without  being 
introduced  into  any  magnetic  field.  This  is 
accomplished  by  introducing  the  lamp  between  two 
metal  plates,  forming,  perhaps,  the  sides  of  a  small 


132  TRANSFORMERS. 

room,  and  each  being  attached  to  one  terminal  of 
the  secondary  already  referred  to. 

An  endless  variety  of  experiments  in  this  line 
have  been  made,  chiefly  by  Mr.  Nichola  Tesla,  to 
whom  chiefly  belongs  the  credit  of  investigation 
in  this  direction. 

The  results  obtained  are  very  interesting,  and 
all  tend  to  prove  that  the  rules  governing  the 
action  of  electricity  as  we  understand  them,  while 
fixed  and  certain,  only  apply  within  what  are 
probably  quite  narrow  limits.  These  experiments 
point  to  the  future  utilization  of  electricity  for 
illuminating  purposes  in  ways  which  are  not  as  yet 
known  to  us,  and  which  will  probably  be  as  greatly 
in  advance  of  present  systems  as  our  existing 
methods  are  in  advance  of  those  of  one  hundred 
years  ago. 

Mr.  Tesla  has  successfully  reproduced,  on  a  small 
scale,  many  of  nature's  marvelous  electrical  phe- 
nomena, and  it  is  probable  that  yet  more  wonder- 
ful discoveries  are  still  to  come.* 

2.    THE  "HEDGEHOG"  TRANSFORMER. 

The  "Hedgehog"  transformer  is  the  invention 
of  Mr.  James  Swinburne,  the  well-known  English 
electrician,  and  was  the  outcome  of  his  theory  that 

*  For  further  information  relative  to  these  experiments  we  would 
refer  the  reader  to  the  Proceedings  of  the  American  Institute  of  Elec- 
trical Engineers,  1891. 


APPENDICES.  133 

the  iron  and  hysteresis  losses  were  more  serious  in 
the  transformer  than  the  C2R  loss.  He  argued, 
therefore,  that  an  open  circuit  transformer,  with 
greatly  reduced  iron,  would  be  more  efficient,  even 
though  the  copper  would  have  to  be  greatly  in- 
creased to  obtain  the  same  induction. 

The  iron  loss  is  without  doubt  reduced  in  the 
construction  adopted  by  Mr.  Swinburne  (See 
Chapter  V),  for  not  only  is  the  sectional  area  of  iron 
reduced,  but  being  an  open  circuit  transformer  the 
outside  iron  is  entirely  wanting,  thus  reducing  the 
total  amount  of  iron  to  about  one-third  that  used 
in  a  closed  circuit  transformer  of  similar  capacity. 

Thus  far  the  theory  is  correct,  for  the  "  Hedge- 
hog "  transformer  has  shown,  in  careful  tests,  that 
its  actual  iron  losses  amount  to  considerably  less 
than  two  per  cent  of  full  load.  The  change  in  the 
arrangement  of  iron,  however,  greatly  increases 
the  loss  in  the  winding,  more  turns  being  needed 
to  obtain  the  same  results.  So  that  the  actual  total 
efficiency  of  the  "  Hedgehog,"  according  to  Mr. 
Swinburne  himself,  proved  to  be  about  87  per 
cent.  To  somewhat  reduce  the  magnetic  resist- 
ance incident  to  the  use  of  an  open  iron  circuit, 
the  ends  of  the  wire  core  are  spread  out  as  pre- 
viously shown  in  Fig.  20,  Chapter  V,.  to  equally 
distribute  the  magnetic  lines  through  a  broad  path 
in  the  surrounding  air,  for  it  is  generally  accepted 
as  true  that  the  magnetic  resistance  of  air  is  rela- 


134  TRANSFORMERS. 

tively  low  when  the  magnetic   induction,  or  the 
magnetic  current  through  a  given  area,  is  small. 

The  construction  of  the  "  Hedgehog "  trans- 
former is  simple  in  the  extreme.  The  iron  wire  of 
the  core  is  built  up  around  a  brass,  or  gun  metal 
back-bone,  one  end  of  which  is  spread  out  to  form 
legs,  and  the  other  to  hold  a  connection  board. 
The  windings  being  placed  over  the  iron,  the  whole 
transformer  is  enclosed  within  an  earthenware  jar 
or  case.  Earthenware  was  selected  for  this  pur- 
pose because,  being  an  open  circuit  transformer, 
an  iron  case  would  at  once  become  magnetized  by 
the  core,  while  a  case  of  any  metal  would  be 
subject  to  Foucault  currents  and  would  waste 
much  energy. 

3.      THE   ELECTRIC    WELDING    MACHINE. 

An  ingenious  and  valuable  application  of  the 
transformer  principle  is  the  Electric  Welding  Ma- 
chine. This  is  a  transformer  so  constructed  as  to 
generate  enormous  current  volume  in  the  second- 
ary, with  very  little  pressure.  The  secondary  coil 
consists,  as  a  rule,  of  but  one  turn  of  heavy  cop- 
per, generally  a  casting.  One  end  of  this  is 
movable,  being  usually  made  in  the  form  of  a  slid- 
ing carriage,  moving  upon  the  solid  portion  of  one 
end  of  the  secondary. 

Each  end  of  the  secondary  carries  a  clamp  or 
vice.  These  clamps  are  placed  directly  opposite 


APPENDICES.  135 

one  another,  one  being  fixed  and  the  other  moving 
with  the  sliding  carriage.  The  two  pieces  of  metal 
to  be  welded  together  being  fixed  in  the  clamps 
opposite  and  parallel,  as  required,  the  movable 
clamp  is  drawn  forward  toward  the  other,  which, 
brings  the  objects  to  be  welded  together  into  con- 
tact, completing  the  circuit  of  the  secondary 
through  them. 

The  current  passing  through  the  secondary  turn 
being  greatly  in  excess  of  the  true  carrying  capac- 
ity of  the  articles  to  be  welded  together  and,  owing 
to  their  very  small  length  between  the  clamps, 
their  resistance  not  being  sufficient  to  materially 
cut  the  current  down,  they  are  speedily  heated  to 
the  melting  point  at  the  point  of  contact  and  high- 
est resistance.  The  two  ends  are  then  forced  to- 
gether while  molten,  and  the  two  objects  are  at 
once  welded  into  one. 

The  welding  machine  is  made  in  many  styles, 
according  to  the  purpose  for  which  it  is  designed. 
Wire,  chain,  pipe,  rod,  axles,  tires,  projectiles,  etc., 
are  all  welded  successfully  and  with  perfect  ease. 
Cast,  as  well  as  wrought  metals,  may  be  welded, 
as  also  may  unlike  metals,  such  as  copper  and  steel. 

The  machines  are  designed  according  to  the 
work  they  are  to  do,  the  larger  and  more  powerful 
ones  containing  many  mechanical  features  of  great 
interest.  The  closing  of  the  weld  is  generally 
accomplished  in  the  larger  machines  by  means  of 


136  TRANSFORMERS. 

hydraulic  pressure,  and  water  circulation  is  pro- 
vided to  keep  the  secondary  and  movable  carriage 
thoroughly  cool.  The  welding  machine  has  a  wide 
field  of  usefulness,  and  though  but  a  recent  inven- 
tion has  already  become  well  known. 

'4.      THE    DIRECT    CURRENT   TRANSFORMER. 

The  statement  has  been  made  throughout  this 
volume  that  electrical  transformation  could  be 
accomplished  only  by  means  of  alternating,  pul- 
sating or  intermittent  currents.  This  is,  perhaps, 
not  literally  true,  although  practically  so. 

There  is  a  system,  however,  whereby  transfor- 
mation is  accomplished  in  connection  with  direct 
current,  but  only  mechanically.  Stated  briefly,  it 
consists  simply  of  an  electric  motor,  operating  on 
a  high  potential  circuit,  and  driving  a  dynamo 
which  generates  at  any  potential  that  may  be  de- 
termined upon.  Thus,  instead  of  energy  being 
transformed  directly  from  electrical  power  of  one 
pressure  to  electrical  power  of  another,  it  must  be 
converted  first  into  mechanical  energy  or  motion, 
and  this  again  to  electrical  power  of  the  pressure 
required. 

Machines  have  been  designed  whereby  both 
transformations  are  accomplished  in  one  piece  of 
apparatus,  both  the  motor  (primary)  and  dynamo 
(secondary)  windings  being  placed  upon  a  single 
armature,  the  same  fields  serving  both  for  dynamo 


APPENDICES.  137 

and  generator.  The  armature  is,  of  course,  pro- 
vided with  two  commutators  and  sets  of  brushes, 
one  for  the  motor  and  another  for  the  dynamo 
winding,  the  two  being  as  absolutely  distinct  as  if 
carried  upon  separate  armatures. 

While  necessarily  somewhat  less  efficient  than 
true  electrical  transformers  of  correct  design,  this 
electro-mechanical  converter  is,  in  certain  cases, 
extremely  useful  and  valuable,  for,  as  has  been 
previously  stated,  alternating  current  has  not,  gen- 
erally speaking,  been  successfully  applied  to  the 
distribution  of  power  for  mechanical  purposes. 

Thus,  when  it  is  desired  to  carry  power  for  the 
operation  of  motors  for  long  distances,  as,  for  ex- 
ample, when  a  water  power  in  a  remote  location  is 
to  be  utilized  to  operate  stationary  motors,  or  street 
cars,  then  the  energy  may  be  transmitted  as  direct 
current  of  high  potential  through  long  distances, 
and  over  light  wire,  with  small  loss,  being  reduced 
to  the  required  pressure  by  means  of  one  or  more 
motor-transformers  situated  at  a  convenient  centre 
of  distribution. 

5.      STATION  TRANSFORMERS. 

It  is  customary  to  have  upon  the  switch-board 
of  every  alternating  dynamo  a  small  transformer, 
which  is  mounted  upon  a  base  or  back,  instead  of 
being  enclosed  within  a  case,  and  these  are  known 
as  station  transformers. 


133 


TKANSFOHMEKS. 


FIG.  38. 


APPENDICES.  139 

These  transformers  are  constructed  with  special 
care  as  regards  regulation,  etc.,  and  have  the  same 
ratio  of  transformation  as  the  transformers  chiefly 
in  use  upon  the  line. 

Volt-meters,  to  measure  high  potentials,  are 
delicate  and  expensive,  consequently  the  switch- 
board volt-meter  is  placed  upon  the  secondary  of 
the  station  transformer  and  indicates  the  potential 
of  the  secondary  circuits.  The  volt-meter  and  the 
two  or  three  lights  which  serve  to  illuminate  the 
switch-board  constitute  the  load  carried  by  the 
station  transformer,  this  load  being,  of  course, 
practically  constant. 

An  excellent  illustration  of  a  station  transformer 
is  shown  in  the  accompanying  cut,  Fig.  38. 

6.      CONSTANT   CURRENT  TRANSFORMERS. 

In  addition  to  the  transformers  which  have  been 
mentioned,  designed  to  operate  upon  constant  cur- 
rents, transformers  have  been  successfully  con- 
structed to  give  a  constant  current  and  varying 
potential  at  the  secondary,  with  the  primary  upon 
a  constant  potential  circuit. 

Such  transformers  are  designed  to  operate  arc 
lamps  upon  incandescent  circuits.  This  result  is 
obtained  by  especial  design  and  construction,  and 
further  mention  of  it  is  purposely  avoided,  lest  it 
should  prove  confusing  and  irrelevant. 


140  TRANSFORMERS. 

7.    UNDERWRITERS'  RULES. 

The  following  rules  are  an  extract  from  the 
Rules  and  Regulations  adopted  by  the  New  Eng- 
land Insurance  Exchange  and  the  Boston  Fire 
Underwriters'  Union,  for  electric  lighting,  as  at 
present  in  force. 

The  rules  in  use  throughout  the  various  States 
of  the  Union  vary  somewhat  from  these  in  detail 
but  are  the  same  in  general  character.  These  reg- 
ulations are  of  great  importance  and  should  be 
carefully  noted  and  closely  followed. 

Only  such  rules  are  presented  here  as  apply 
directly  to  the  application  of  transformers.  For 
the  complete  text  of  the  regulations  the  reader  is 
referred  to  the  official  publication. 

SECONDARY   GENERATORS  OR  CONVERTERS. 

Converters  must  not  be  placed  inside  of  any  building. 
They  may  be  placed  on  the  outer  walls  when  in  plain  sight 
and  easy  of  access,  but  must  be  thoroughly  insulated  from 
them.  If  placed  on  wooden  walls,  or  the  woodwork  of  stone 
or  brick  buildings,  the  insulation  must  be  fire-proof.  When 
an  underground  service  is  used,  the  converter  may  be  put  in 
any  convenient  place  that  is  dry  and  does  not  open  into  the 
interior  of  the  building ;  this  location  must  have  the  approval 
of  the  inspector  before  the  current  is  turned  on. 

The  converter  should  be  enclosed  in  a  metallic  or  non- 
combustible  case. 

If  for  any  reason  it  becomes  necessary  that  the  primary 
wires  leading  to  and  from  the  converter  should  enter  a 
building,  they  must  be  kept  apart  a  distance  of  not  less  than 
twelve  inches,  and  the  same  distance  from  all  other  con- 


UNDERWRITERS'  RULES.  141 

ducting  bodies.  The  insulation  of  the  wire  must  be  of  the 
very  best. 

Safety  fuses  must  be  placed  at  the  junction  of  all  feeders 
and  mains,  and  at  the  junction  of  mains  and  branches  where 
necessary,  also  in  both  the  primary  and  secondary  wires  of 
the  converter,  in  such  a  manner  as  not  to  be  affected  by  the 
heating  of  the  coils.  Secondary  wires,  after  leaving  the 
converter,  will  be  subject  to  rules  already  given  for  services, 
inside  wiring,  etc. 

Any  provision  for  grounding  the  secondary  circuit  by 
means  of  "film  cut-out"  or  other  approved  automatic  device 
will  be  approved.  A  permanent  ground  will  not  be  approved. 

SECONDARY  SYSTEMS. 

In  these  systems  where  alternating  currents  of  high  elec- 
tro-motive force  are  used  on  the  main  lines,  and  secondary 
currents  of  low  electro-motive  force  are  developed  in  local 
"converters"  or  "transformers,"  it  is  important  that  the 
entire  primary  circuit  and  the  transformers  should  be  ex- 
cluded from  any  insured  building,  and  be  confined  to  the 
aerial  line  (the  transformers  being  attached  to  the  poles  or 
the  exterior  of  the  buildings)  or  to  underground  conduits  if 
such  are  used,  or  placed  in  fire-proof  vaults  or  exterior 
buildings. 

In  those  cases,  however,  where  it  may  not  be  possible  to 
exclude  the  transformers  and  entire  primary  from  the  build- 
ing, the  following  precautions  must  be  strictly  observed : 

The  transformer  must  be  constructed  with  or  inclosed  in 
a  fireproof  or  incombustible  case,  and  located  at  a  point  as 
near  as  possible  to  that  at  which  the  primary  wires  enter 
the  building.  Between  these  points  the  conductors  must  be 
heavily  insulated  with  a  coating  of  approved  waterproof 
material  and,  in  addition,  must  be  so  covered-in  and  pro- 
tected that  mechanical  injury  to  them,  or  contact  with  them, 
shall  be  practically  impossible. 

These  primary  conductors,  if  within  a  building,  must  also 
be  furnished  with  a  double-pole  switch,  or  separate  switches 


142  TRANSFORMERS. 

on  the  ingoing  and  return  wires  and  also  with  automatic 
double-pole  cut-out  where  they  enter  the  building  or  where 
they  leave  the  main  line,  on  the  pole  or  in  the  conduit.  The 
switches  above  referred  to  should,  if  possible,  be  inclosed  in 
secure  and  fireproof  boxes  outside  the  building. 

In  the  case  of  isolated  plants  using  the  secondary  system, 
the  transformers  must  be  placed  as  near  to  the  dynamos  as 
possible,  and  all  primary  wires  must  be  protected  in  the 
same  manner  as  is  indicated  in  the  second  paragraph  above. 


143 


GLOSSARY. 


ELECTRICAL    TERMS    NOT    EXPLAINED     IN 
THE   PRECEDING  CHAPTERS. 

Ampere. — The  unit  of  electric  current.  A  current 
of  just  sufficient  strength  to  deposit  .005084  grains  of 
copper  per  second. 

Electro -Motive  Force. — Generally  expressed  as 
E.  M.  F.  (See  Voltage.) 

Kapp  Lines. — A  unit  of  lines  of  magnetic  force. 

Multiple. — Synonymous  with  Parallel.  (See  Chap- 
ters I  arid  VI.) 

Ohm. — The  unit  of  electrical  resistance.  A  resist- 
ance through  which  one  volt  can  just  force  one 
ampere. 

Parallel. — See  Multiple. 
Potential. — See  Voltage. 

Series. — Lamps  or  other  pieces  of  apparatus  are  in 
series  when  the  same  and  whole  current  passes 
through  them  all,  one  after  another.  (See  Chapters  I 
and  VI.) 


144  GLOSSARY. 

Voltage. — Synonyms :  Potential,  Electro-Motive 
Force,  Pressure,  etc.  The  number  of  volts  pressure 
present  at  any  given  point  in  a  circuit. 

"Watt. — The  unit  of  electric  power,  or  the  volt- 
ampere.  The  volts  multiplied  by  the  amperes  in  use 
equal  the  watts. 


INDEX.  145 


INDEX. 


A 

Alternating  current 17,  19(    22 

Analysis  of  iron .'    82 

Asbestos  paper,  use  of 89 

Attraction,  molecular * 52 

B 

Baking 90,  108,  109 

Banking  in  multiple 98 

in  series 100 

three  wire 101 

Binding  bolts 85 

Blocks,  terminal 91 

Box,  transformer 91 

Burr  on  plates 83 

c 

Calorimeter 51,  53 

Carbon 82 

Capacity,  transformer  required 97 

Case,  transformer 91 

Coil,  reactive 39,  45 

induction 26 

Faraday  induction 64,  80 

Ruhmkorff 64,  81 

Coils,  ends  of 89 

Cobalt 40 

Connections,  secondary ...  108 

Commutator,  function  of 

Constant  current  transformer 139 

Construction,  rules  for 94 

Core,  form  of 73 

joining  of 76 


146  INDEX. 


Core,  open  circuit 65,  81 

building  of 84 

grounding  of 105,  123 

wire 80 

Copper  tape,  use  of 87 

Cost,  influence  of 67 

Crossing  of  leads 91,  94 

Currents,  magnetic 39 

D 

Danger  from  grounds 105 

Deptford  Station 128 

Devices,  safety 92 

Dies  for  punching 82 

Dick  and  Kennedy's  early  transformer 67 

Direct  current 18 

transformers 136 

Direction  of  current 15 

Discharge,  10,000  volt 128 

Distribution,  electrical 15 

Dynamo,  principle  of 12 

E 

Eddy  currents 12,  48 

Efficiency  of  transformers .    62 

curve 61 

Electron 14 

F 

Faraday  coil 64,  80 

Faraday's  discoveries 63 

Ferranti  converter 72,  110 

Ferranti's  early  transformer 66 

Fiber,  vulcanized 89 

Field  of  force 12 

Filings,  iron 40 

Force,  lines  of 14,  40 

Formulae,  Hopkinson's 55 

Fort  Wayne  Electric  Co 118 

Foucault  currents 12,  48 

Friction,  molecular 53 

Fuse,  main  circuit 100 

Fuses 38 

location  of 106,  108 

replacing  of 92,  108 


INDEX.  147 

Fuses,  rubber  covered 106,  108 

sub-circuit 100 

G 

General  Electric  Co 121 

Gloves,  rubber 108 

Goulard  and  Gibbs,  distribution 66 

Grounding  of  core 105,  123 

H 

Hedgehog  transformer 72,  81,  132 

High  voltages 128 

measurement  of 129 

Humming  of  transformer 95,  107 

Hysteresis 51 

I 

Improvement,  direction  of 72 

Induction,  electrical 10,  14,  17 

coil     26,  80 

self 32,  39,  46 

mutual 34,  46 

Inertia,  electrical 10,  39 

magnetic 52 

Intermittent  current 17,  19 

Interrupter 25 

Insulation 90,  94 

Insulation  in  lamination 84 

oil 92,  105,  123 

puncturing  of 92,  105 

of  winding 86,  89 

wood  for 90 

Iron,  complete  circuit  of 41 

analysis  of 82 

English 82 

lamination  of 50 

filings 40,  95 

permeability  of 40 

selection  of 82 

wrought,  characteristics  of 43 

J 

Jablochkoff,  distribution 66 

Jar,  advantage  of 103,  108 

Joints  in  windings 88 


148  INDEX. 

K 

Kapp  lines 41 

Kennedy's  transformer 66 

L 

Lag 11 

Lamp,  incandescent 17 

Lathe,  winding 86 

Lamination  of  iron 50 

Law,  Ohms 46 

Leads,  crossing  of 91,  94 

Lightning,  effect  of 104,  106 

discharge,  potential  of 106 

Lines  of  force 14,  40,  41 

Kapp 41 

Location  of  transformers 93,  103 

Loss,  C2R 16 

in  converters 45 

percentage  of 54 

M 

Magnetic  circuit,  resistance  of 66 

currents 39 

Magneto 93 

-motive  force 57 

Mandril,  winding 86 

Mica,  use  of 89 

Molecular  attraction 52 

friction 53 

Multiple,  banking  in 98 

arrangement 27 

Mutual  induction 34,  46 

N 

National  Electrical  Mfg.  Co 115 

transformer 115 

Nickel 40 

o 

Ohm's  law 46 

Oil  insulation 92,  105,  123 

P 

Paccinotti  ring 87 

Paper,  asbestos 89 


INDEX.  149 

Paper,  shellaced gg 

Parallel  arrangement .....'.,  27 

Phosphorus 

Pine '.'.'.'.'.'.'...'.'.  90 

Plates,  punching  of ...   82 

Polarity,  change  of 52 

Potential,  best  to  use 98 

difference  of 10 

Primary  circuits,  handling  of 108 

coil,  character  of 15,  17 

Pulleys,  tension 86 

Pulsating  currents 17,  19,  23 

Punching  of  plates 82 

Puncturing  of  insulation 105 

R 

Ratio  of  diameter  to  circumference 56 

of  windings 59 

Reactive  coil 39,  45 

Regulation,  self 34 

Resistance  of  circuits 16 

Ring-shaped  core 78 

Ribbon,  silk,  use  of 87 

Rubber  tape,  use  of 87 

Ruhmkorff  coil 64,  81 

Rules  for  construction 94 

for  installation 108 

Underwriters' 108,  140 

s 

Saturation  point 42 

Safety  devices 92 

Secondary  coil,  character  of 15,  17 

Sectional  area  of  wire 94 

Self-induction 32,  89,  46 

Series  arrangement 27 

Silicon 82 

Slattery  transformer 118 

Stanley  Electrical  Manufacturing  Co 118 

transformer 118 

Stanley's  early  transformer ' 67 

Steel,  sheet 43 

use  of  for  cores 82 

Step-up  transformer 26,  107,  128 

St.  Elmo's  fire 131 

Station  transformer 137 


150  INDEX. 

Swedish  iron 82 

Swinburne's  transformer 72,  132 

Symbols  assumed 55 

T 

Tape,  copper 87 

rubber 87 

Taping  of  coils 88 

Teak,  use  of 90 

Tension  pulleys 86 

Terminal  blocks 91 

Tesla's  experiments 128 

Testing  of  transformers 93 

Thomson-Houston  transformer 121 

Three-wire  arrangement 101 

u 

Underwriters'  rules 108,  140 

V 

Vibration  and  hysteresis 52,  103 

w 

Water,  analogous  to  electricity 16 

Weight  of  transformer  per  useful  watt 60 

Welding  machine 134 

Westinghouse  converter 125 

Winding,  methods  of 76,  85 

Windings,  proportioning  of 60 

ratio  of 59 

Wire,  coiling  of 32 

Wood  for  insulation 90 

Working  point 42 

z 

Zipernowski  and  Derri's  early  transformer 70 


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pages.  250  Illustrations.  12010.  Cloth.  The  best  and  most  complete  book  of 
the  present  time,  and  is  particularly  adapted  for  the  use  of  students.  Contains 
20  chapters  of  the  best  and  latest  experiments,  also  complete  working  directions 
for  building  all  kinds  of  electrical  machinery.  Price,  $2.00,  Cloth  Bound. 


"  A  Practical  Treatise  on  the  Incandesctnt  Lam}?  by  J.  E.  Randall, 
Electrician  of  the  Incandescent  Lamp  Department  of  the  Thompson-Houston 
Co.  Illustrated.  This  is  the  only  work  that  explains  in  a  practical  manner  the 
manufacture  of  the  Incandescent  Lamp,  and  should  be  owned  by  every  Electric- 
ian and  student  interested  in  the  subject.  Price,  50  cents,  Cloth  Bound. 


"  A  Practical  Treatise  on  Electro-Plating,"  by  Edward  Trevert.     Just  the 
book  for  Amateurs.     Fully  Illustrated.    Sent  to  any  address  on  receipt  of  price. 

Price,  50  cents,  Cloth  Bound. 

"  Electric  Motor  Construction  for  A  ntateurs"  by  C.  D.  Parkhurst.  Illus- 
trated. Just  the  book  for  beginners  or  for  anybody  wishing  to  construct  their 
own  electrical  apparatus.  Giving  complete  directions  and  working  drawings  for 
making  an  electric  motor  for  running  sewing  machines,  small  lathes,  etc.  Also 
gives  directions  and  drawings  for  building  an  electric  battery  to  furnish  current 
for  the  motor. Price,  $1.00,  Cloth. 

"•A  Hand  Book  of  Wiring  Tables,"  for  Arc,  Incandescent  Lighting  and 

Motor  Circuits,  by  A.  E.  Watson.    This  book  gives  a  large  number  of  Formula- , 

Rules  and  Tables  for  Wiring,  and  is  illustrated  with  numerous  diagrams.  It  also 

contains  a  large  amount  of  practical  information  upon  the  subject,  up  to  date. 

Price,  75  cents,  Cloth. 

"How  to  Make  and  Use  Induction  Coils,"  by  Edward  Trevert.  The 
only  American  book  upon  Induction  Coils.  It  is  fully  illustrated,  and  every 
student  of  electricity  should  own  one.  Bound  in  a  neat  cloth  binding. 

Price,  50  cents,  postpaid. 

"  Questions  and  Answers  About  Electricity."  A  first  book  for  students. 
Theory  of  Electricity  and  Magnetism.  Edited  by  E.  T.  Bubier,  2d.  Authors: 
T.  O'Connor  Sloane,  A.  M.,  E.  M.,  PH.  D. ;  Caryl  D.  Haskins,  M.  I.  E.  E. ; 
A.  E.  Watson;  Edward  Trevert.  Illustrated.  Contents:  Chapter  I. — 
Theory  of  Electricity.  II. -Theory  of  Magnetism.  III. -Voltaic  Batteries. 
IV. -Dynamos  and  Motors.  V.  -  Electric  'Lamps.  VI. -Miscellaneous 
Electrical  Apparatus.  VII.  —  Electrical  Measurement. 

Price,  Cloth  Bound,  50  cents. 

All  Books  sent  postpaid  on  receipt  of  price. 

Send  Money  by  P.  O.  order  or  registered  letter  at  our  risk. 


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